Ở một loài thực vật, alen A quy định quả tròn trội hoàn toàn so với alen a quy đinh quà dài; alen B quy định quả ngọt trội hoàn toàn so với alen b quy định quả chua. Hai cây dị hợp về cả hai cặp gen trên giao phấn với nhau, thu được đời con gồm 4 loại kiểu hình trong đó kiểu hình quả tròn, chua chiếm tỷ lệ 24%. Theo lý thuyết, trong tổng số cây thu được ở đời con, số cây có kiểu hình quả tròn, ngọt chiếm tỷ lệ  

A. 54%.

B. 51%.

C. 56%.

D. 24%

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

        Sharks have gained an unfair reputation for being fierce predators of large sea animals. Humanity's unfounded fear and hatred of these ancient creatures is leading to a worldwide slaughter that may result in the extinction of many coastal shark species. The shark is the victim of a warped attitude of wildlife protection; we strive only to protect the beautiful, non-threatening parts of our environment. And, in our efforts to restore only non-threatening parts of our earth, we ignore other important parts.

        A perfect illustration of this attitude is the contrasting attitude toward another large sea animal, the dolphin. During the 1980s, environmentalists in the United States protested the use of driftnets for tuna fishing in the Pacific Ocean since these nets also caught dolphins. The environmentalists generated enough political and economic pressure to prevent tuna companies from buying tuna that had been caught in driftnets. In contrast to this effort on behalf of the dolphins, these same environmentalists have done very little to help save the Pacific Ocean sharks whose population has decreased nearly to the point of extinction.

Sharks are among the oldest creatures on earth, having survived in the seas for more than 350 million years. They are extremely efficient animals, feeding on wounded or dying animals, thus performing an important role in nature of weeding out the weaker animals in a species. Just the fact that species such as the Great White Shark have managed to live in the oceans for so many millions of years is enough proof of their efficiency and adaptability to changing environments. It is time for US humans, who may not survive another 1,000 years at the rate we are damaging the planet, to cast away our fears and begin considering the protection of sharks as an important part of a program for protection of all our natural environment.

With which of the following topics is this passage primarily concerned?

A. Sharks are efficient creatures with bad reputations.

B. Sharks are some of the oldest creatures on earth.

C. Sharks illustrate a problem in wildlife protection.

D. The campaign to save dolphins was not extended to save sharks.

Nêu tác dụng của các chính sách đối nội và đối ngoại của nhà nước phong kiến?