Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 38 to 42.

  Lead poisoning in children is a major health concern. Both low and high doses of paint can have serious effects. Children exposed to high doses of lead often suffer permanent nerve damage, mental retardation, blindness, and even death. Low doses of lead can lead to mild mental retardation, short attention spans, distractibility, poor academic performance, and behavioral problems.

  This is not a new concern. As early as 1904, lead poisoning in children was linked to lead-based paint. Microscopic lead particles from paint are absorbed into the bloodstream when children ingest flakes of chipped paint,plaster,or paint dust from sanding. Lead can also enter the body through household dust, nailbiting, thumb sucking, or chewing on toys and other objects painted with lead-based paint. Although American paint companies today must comply with strict regulations regarding the amount of lead used in their paint, this source of lead poisoning is still the most common and most dangerous. Children living in older, dilapidated houses are particularly at risk.

What does the author imply in the final sentence of the passage?

A. Old homes were painted with lead - based paint. 

B. Lead-based paint chips off more easily than newer paints. 

C. Poor people did not comply with the regulations 

D. Old homes need to be rebuilt in order to be safe for children.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 38 to 42.

  Lead poisoning in children is a major health concern. Both low and high doses of paint can have serious effects. Children exposed to high doses of lead often suffer permanent nerve damage, mental retardation, blindness, and even death. Low doses of lead can lead to mild mental retardation, short attention spans, distractibility, poor academic performance, and behavioral problems.

  This is not a new concern. As early as 1904, lead poisoning in children was linked to lead-based paint. Microscopic lead particles from paint are absorbed into the bloodstream when children ingest flakes of chipped paint,plaster,or paint dust from sanding. Lead can also enter the body through household dust, nailbiting, thumb sucking, or chewing on toys and other objects painted with lead-based paint. Although American paint companies today must comply with strict regulations regarding the amount of lead used in their paint, this source of lead poisoning is still the most common and most dangerous. Children living in older, dilapidated houses are particularly at risk.

The word "dilapidated" is closest in meaning to which of the following?

A. unpainted

B. decorated

C. broken down

D. poorly painted

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 38 to 42.

  Lead poisoning in children is a major health concern. Both low and high doses of paint can have serious effects. Children exposed to high doses of lead often suffer permanent nerve damage, mental retardation, blindness, and even death. Low doses of lead can lead to mild mental retardation, short attention spans, distractibility, poor academic performance, and behavioral problems.

  This is not a new concern. As early as 1904, lead poisoning in children was linked to lead-based paint. Microscopic lead particles from paint are absorbed into the bloodstream when children ingest flakes of chipped paint,plaster,or paint dust from sanding. Lead can also enter the body through household dust, nailbiting, thumb sucking, or chewing on toys and other objects painted with lead-based paint. Although American paint companies today must comply with strict regulations regarding the amount of lead used in their paint, this source of lead poisoning is still the most common and most dangerous. Children living in older, dilapidated houses are particularly at risk.

Which of the following does the passage infer?

A. Paint companies can no longer use lead in their paint. 

B. Paint companies must limit the amount of lead used in their paint. 

C. Paint companies aren't requừed to limit the amount of lead used in their paint. 

D. Paint companies have always followed restrictions regarding the amount of lead used in their paint.

Giải:

a)Số học sinh trung bình của lớp 4A chiếm:

1-(1/8 + 1/2)=3/8 (số học sinh cả lớp)

Phân số biểu thị số học sinh khá hơn số học sinh trung bình là:

1/2-3/8=1/8

Số học sinh của lớp 4A là:

5:1/8= 40 ( học sinh)

b) Số học sinh giỏi của lớp 4A là:

40.1/8=5 ( học sinh)

Số học sinh khá của lớp 4A là:

40.1/2=20 ( học sinh)

Số học sinh trung bình của lớp 4A là:

40-(5+20)=15(học sinh)

Đáp số:5 HS giỏi, 20 HS khá, 12 HS trung bình.

CHÚC BẠN HỌC TỐT.

Ta có:(5x+11y)+2(x-2y)=7x+7y chia hết cho 7

Mà 5x+11y chia hết cho 7

=>2(x-2y) chia hết cho 7

Mà (2;7)=1

=>x-2y chia hết cho 7.

Pin quang điện là nguồn điện, trong đó

A. quang năng được biến đổi trực tiếp thành điện năng

B. cơ năng được biến đổi trực tiếp thành điện năng

C. hóa năng được biến đổi trực tiếp thành điện năng

D. nhiệt năng được biến đổi trực tiếp thành điện năng

Trong nguyên tử kim loại kiềm ở trạng thái cơ bản có số electron lớp ngoài cùng là

A. 4.

B. 3.

C. 1.

D. 2.

Tìm các tính chất không thuộc về khí nitơ?

(a) Hóa lỏng ở nhiệt độ rất thấp (-196^oC);

(b) Cấu tạo phân tử nitơ là  N ≡ N

(c) Tan nhiều trong nước;

(d) Nặng hơn oxi;

(e) Kém bền, dễ bị phân hủy thành nitơ nguyên tử.

A. (a), (c), (d).

B. (a), (b).

C. (c), (d), (e).

D. (b), (c), (e)

Viết phương trình hoá học của các phản ứng xảy ra trong mỗi trường hợp sau:

Toluen tác dụng với hiđro có xúc tác Ni, áp suất cao, đun nóng.