由动词+副词构成的词组，代词作宾语时要用宾格放在中间，如：add up，think over turn on / off / up / down get back write down clean up ， cheer up 等这类动词短语后接接宾语时，有两种情况，1.宾语是名词时，这个名词可以放在短语后，也可以放在短语中间2.宾语是代词时，这个代词可就只能放在短语中间.如：
The radio is too loud . Please turn it down .
The teachers told the kids how to add up numbers.
The teachers told the kids how to add numbers up.
The teacher wrote some numbers on the blackboard and asked the kids to add them up.
They will think over the problem before they make the decision..
The problem is vital，and they are thinking it over.
