Запишите в времени глагола present perfect tense alredy (to be) to the usa. the teacher just (to explain) the new rule. mark alredy (to do) shopping, but he (not to start) cooking yet.

I have already been to the USA.
The teacher has just explained the new rule.
Mark has already done shopping, but he hasn't started cooking yet.

I have already been to the USA. 
The teacher has just explained the new rule.
Mark has already done shopping, but he haven't started cooking yet.