判断下列句子中不定式在句子中的成分.作目的状语or作后置定语or作宾语
I can not think out any good advice to give her.___
I am thirsty.Can I have something to drink?___
Let's go to buy some foog.____
They decided to go on a trip to the Great Wall during the summer vacation.____
Why dont't you get togerther to discuss this question?____