Yesterday it rained heavily when school was over. So we _______ stay in our classroom.
A：should
B：must
C：had to
用配方法解方程x2+4x+1=0时，经过配方，得到（ ）
把海拔相同的各点连接成线叫 ____ ．
I wonder whether my son likes the coat I bought for him.
— Sorry, I won't.
