阅读短文，下列问题

A

    Hemingway was one of the famous writers. He was born in Americain 1899. His father was a doctor and loved sports very much, and his mother taught music. Among the six children in the family, Hemingway was the second oldest.

    Hemingway had written many books in his life. The Old Man and the Sea is one of the most famous books and it is also my favorite. It came out in 1952. The main character in the book is a fisherman. He is an old man and fishes alone. People think he is a man with bad luck, because he doesn't get a fish in eighty-four days. Every evening, he comes home with his empty boat. But the old man believes himself. Then on the eighty-fifth day the old man takes a big fish.Although he meets a lot of trouble, the old man never gives up.

使用显微镜进行观察时，若正好遇上阴天，应选择（  ）