(3) 在疑问句和否定句中表示怀疑、惊奇、不相信的态度。如： Can this green bike be Liu Dong's? How can you believe such a liar like him? (4) 用于肯定句，表示一时的情况，意为：有时候会。如： It can be very hot here in summer. Tom is a clever boy, but he can be dull sometimes.