Pardon? I _____ quite catch you.I said I ______ the song before.
A:didn't, hadn't heard
B:don't, didn't hear
C:didn't, didn't hear
D:won't, hadn't heard
①弄清自己的真实需要 ②征求父母、老师等人的意见
③收集相关的格言警句 ④具体了解两所学校的招生要求、教学条件等
下列没有错别字的一组是( )
有一小球重为15N,将其全部浸没在水中时,它排开的水重为10N,此时它受到的浮力为 ____ N,松手后小球将____ (选填“上浮”、“下沉”或“悬浮”).