Listen ,There are some children knocking ()Mrs Brown is door.a:with,b:to,c:at,d:off.
问题描述：
Listen ,There are some children knocking ()Mrs Brown is door.a:with,b:to,c:at,d:off.
答
at the door 固定词组
答
C，这个是固定搭配
答
at
knock at door 固定搭配.敲门、、
答
C knocking at Mrs Brown's door 有些孩子们在敲布朗夫人的门