Today is Saturday. The weather is warm and sunny. Bob and Jack go to the park. There are many people there. The girl under a big tree is reading a book. Two boys are playing football on the grass. The girl in a red dress is riding a bike. Two women are talking. The man beside these women is playing with a baby. Bob and Jack are beside the river. They are sitting on the chair and drawing pictures.

⑴It's warm and sunny ____       A. are beside the river.

⑵There are many people ____    B. are talking.

⑶Two boys ____                 C. in the park.

⑷Two women ____              D. are playing football on the grass.

⑸Bob and Jack ____             E. on Saturday.

光学显微镜是一种常用的观察工具．进行观察时，对所观察生物材料的要求是（  ）