如果最简二次根式$\sqrt{1+a}$与$\sqrt{4a-2}$是同类二次根式，那么a=____ 

如图为运动员掷铅球的情景，铅球由运动员掷出后在空中飞行（不计空气阻力），则（   ）

A是____，B是____，C是____，D是____．

填写单词 根据句子意思, 在空格中填写适当的单词, 使句子完整、正确。

Here are four seasons in a year — spring, ____ , autumn and winter.

Frank was ____ in 2000. He is fifteen this year.

It's 12:00 at noon. It's time for students to have____ in the dining hall.

To keep____ , you'd better exercise every day and eat more fruit and vegetables.

In China, many children are taken____ of by their grandparents in the village.

— I've ____ been to a water park before.

— Me neither.

What does John want to be when he____ up?

A boy ____  himself in P. E. class. The teacher and two students took him to the  hospital at once.

“笛弄晚风三四声”中“弄”的意思是（   ）