a picnic 是指某一野餐.例句: Have a picnic this weekend is a good idea. 这个周末进行(一次)野餐是个好主意. picnics (多次的)野餐.例句: People in California like to have picnics in the summer. 加州人喜欢在夏季野餐(多次的). picnics are fun 指一般来说野餐都有乐趣,不是指某一野餐.
have a picnic[英][hæv ə ˈpiknik][美][hæv e ˈpɪknɪk]去野餐; Let's have a picnic. 让我们去野餐吧。 have picnics野餐 And then we'll have picnics under this tree. 我们就可以在大树下野餐了