1.Mary _____ an English song in her room last night.

题目

1.Mary _____ an English song in her room last night.
A.was heard to sing B.was heard singing 答案为什么是B呢?
2.Mary ____ some songs in her room in the morning.我知道,此题答案是is heard to sing

答案

被听见正在唱
第二题用is heard to sing 用于一般情况,正常时态,
第一题 last night 特指昨晚.