用括号中动词的正确形式填空'I __(explain)this to you several times already

'I _have explained 完成时表示一段时间内重复做某事_(explain)this to you several times already,'said the teacher.'I hope you_understand 虚拟,用原形_(understand)it now.'Then he loooked at a little boy at the back of the class.'Are you listening 表示一个状态,所以用现在进行时_(listen),Jones?'he asked.'Here is a simple problem:"Sally has worked后面有for引导的时间状语,所以要用完成时表示动作一直持续(work)in an office for thirty-four weeks.In that time,she_earned_(earn)300yuan a week.How much_has_she_earned后面是“到目前为止”也要用完成时_(earn)so far.
'Please,sir,'Jones answered,'I can only answer your first question.I _am not listening表示状态,跟前面一样_(not listen).'

have explained
understand
are listening
has worked
earned
has earned
didn't listen

have explained
understand
are listening
has worked
earned
has earned
didn't listen