tìm GTNN của các biểu thứ sau

C=x²+7x+11

D=2x²+4x+15

Tìm GTLN của các biểu thức sau

C=-x²+3x+1

D=-2x²+8x-6

1. Mục đích lớn nhất của tác giả khi viết văn bản thông tin về ngày Trái Đất năm 2000 là gì?

2. Tác dụng của việc dùng dấu phẩy trong nhan đề ôn dịch, thuốc lá là gì?

3. Theo em câu văn '' nếu giặc đánh như vũ bão thì không đáng sợ đáng sợ là giặc gặm nhấm như tầm ăn dâu " dử dụng biện pháp nghệ thuật nào?

4. Nêu tác hại của thuốc lá được đề cập đến trong bài viết ôn dịch, thuốc lá là gì?

Trong các phản ứng hóa học sau, phản ứng nào sai?

A.  SiO 2 + 4 HF → SiF 4 + 2 H 2 O

B. SiO 2 + 4 HCl → SiCl 4 + 2 H 2 O

C. SiO 2 + 2 C → t 0 Si + 2 CO

D. SiO 2 + 2 Mg → t 0 2 M gO + Si

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 31 to 37.

Because writing has become so important in our culture, we sometimes think of it as more real than speech. A little thought, however, will show why speech is primary and writing secondary to language. Human beings have been writing (as far as we can tell from surviving evidence) for at least 5000 years; but they have been talking for much longer, doubtless ever since there have been human beings.

          When writing did develop, it was derived from and represented speech, although imperfectly. Even today there are spoken languages that have no written form. Furthermore, we all learn to talk well before we learn to write; any human child who is not severely handicapped physically or mentally will learn to talk: a normal human being cannot be prevented from doing so. On the other hand, it takes a special effort to learn to write. In the past many intelligent and useful members of society did not acquire the skill, and even today many who speak languages with writing systems never learn to read or write, while some who learn the rudiments of those skills do so only imperfectly.

          To affirm the primacy of speech over writing is not, however, to disparage the latter. One advantage writing has over speech is that it is more permanent and makes possible the records that any civilization must have. Thus, if speaking makes us human, writing makes us civilized.

Question:Normal human beings______.

A. learn to talk after learning to write.

B. learn to write before learning to talk.

C. learn to write and to talk at the same time.

D. learn to talk before learning to write.