the boys enter the movie theatre,__(sing) songs,they are very happy.the boys enter the movie theatre,__(sing) songs.They are very happy.请讲解怎么判断时态，即为什么是xx答案
问题描述：
the boys enter the movie theatre,__(sing) songs,they are very happy.
the boys enter the movie theatre,__(sing) songs.They are very happy.
请讲解怎么判断时态，即为什么是xx答案
答