Unit 2 Topic 1Pollution has caused too many problems .Section D
It _____ (be) beautiful in the past. Kangkang _______ (go) there two years ago.
The flowers and grass ___________ (go).Everything _____________ (change).
Mrs. Zhou ____________ (be) like this since last week. She ______________ (not see) a doctor yet.
was
went
have gone
has changed
has been
hasn’t seen
Simple past 强调过去
Present perfect 强调现在
They are caused by pollution.
There are many kinds of pollution around us,
air pollution
lig ...