Playing on a frozen sports field sounds like a lot of fun. Isn' t it rather risky,().

单项选择题The traffic rule says young children under age four and () less that 40 pounds must be in a child safety seat.

A. being weighed
B. to weigh
C. weighed
D. weighing

单项选择题For many years, people () electric cars. However, making them has been more difficult that predicted.

A. had dreamed of
B. have dreamed of
C. dreamed of
D. dream of