An umbrella is useful when it rains heavily.

下大雨时雨伞很有用。

同一单元的其他句子

• The cat is sleeping on the sofa.猫在沙发上睡觉。
• I have an apple and a banana.我有一个苹果和一个香蕉。
• The students are studying in the library.学生们正在图书馆学习。
• She is a doctor at the hospital.她是医院里的一名医生。
• The children are playing in the park.孩子们在公园里玩。