khi cho giao phối giữa cây thuần chủng có quả đỏ,lá xoăn với cây thuần chủng có quả vàng ,lá thẳng thu được tất cả các loại cây F1 thu được quả đỏ,xoăn

a,hãy dựa vào định luật nào đó của menđen để giải thích ra kết luận về tính trạng trội,tính trạng lặn,đồng thời lập quy ước gen

b,trong 1 phép lai F giữa cây quả đỏ là 50% số cây quả đỏ,lá xoăn và 5% số đó là thẳng.Biện luận và lập sơ đồ lai:biết 2 cặp tính trạng và màu quả và dạng là di truyền độc lập với nhau

Cho tam giác ABC vuông ở A, có cạnh BC cố định. Gọi I là giao điểm của ba đường phân giác trong. Tìm quỹ tích điểm I khi A thay đổi.

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 36 to 42.

          The countryside of Britain is well known for its beauty and many contrasts: it bare mountains and moorland, its lakes, rivers and woods, and its long, often wild coastline. Many of the most beautiful areas are national parks and are protected from development. When Britain people think of the countryside they think of farmland, as well as open spaces. They imagined cows or sheep in greenfield enclosed by hedges or stone walls and field of wheat and barley. Most farmland is privately owned but is crossed by a network of public footpaths.
          Many people associate the countryside with peace and relaxation. They spend their free time walking or cycling there, or go to the country for a picnic or a pub lunch. In summer people go to fruit farms and pick strawberries and other fruit. Only a few people who live in the country work on farms. Many commute to work in towns. Many others dream of living in the country, where they believe they would have a better and healthier lifestyle.
          The countryside faces many threats. Some are associated with modern farming practices, and the use of chemical harmful to plants and wildlife. Land is also needed for new houses. The green belt, an area of land around many cities, is under increasing pressure. Plans to build new roads are strongly opposed by organizations trying to protect the countryside. Protesters set up camps to prevent, or at least delay the building work.
          America has many areas of wild and beautiful scenery, and there are many areas, especially in the West in States like Montana and Wyoming, where few people living. In the New England states, such as Vermont and New Hampshire, it is common to see small farm surrounded by hills and green areas. In Ohio, Indianan, Illinoisan and other Midwestern states, field of corns or wheat reach to the horizon and there are many miles between towns.
          Only about 20% of Americans live outside cities and towns. Life may be difficult for people who live in the country. Services like hospitals and schools may be further away and going shopping can mean driving long distances. Some people even have to drive from their homes to the main road where their mail is left in a box. In spite of the disadvantages, many people who live in the country say that they like the safe, clean, attractive environment. But their children often move to a town or city as soon as they can

Which of the following threatens the countryside in Britain?

A. The green belt around cities

B. Protest against building work

C. Modern farming practices

D. Plants and wildlife

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.

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

Phát biểu nào sau đây là không đúng?

A. Hạt êlectron là hạt có mang điện tích âm, có độ lớn 1 , 6 . 10 - 19  (C).

B. Hạt êlectron là hạt có khối lượng  m = 9 , 1 . 10 - 31 ( kg )

C. Nguyên tử có thể mất hoặc nhận thêm êlectron để trở thành ion.

D. êlectron không thể chuyển động từ vật này sang vật khác

Mark the letter A, B, C, or D on your answer sheet to indicate the most suitable response to complete each of the following exchanges.
- Roger: “Wow! You look terrific in that new dress!” - Tina: “________”

A. Oh, what a pity!

B. I’m afraid so!

C. Thank you. I’m glad you think so.

D. Why dare you say so?