According to the passage, which of the following words best describes the efforts of the marine biologists working with oysters? A. Persistent B. Intermittent C. Traditional D. Fruitless

:  A

Dựa vào đoạn “So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940’s a significant breakthrough was made” ®những nhà sinh vật học đã nỗ lực một cách kiên trì ® chọn A