几道关于非谓语动词的高中英语选择题,请说明为什么,

 Robert is said_____ abroad,but I don’t know what country he studied in.
  A.to have studied     B.to study                 C.to be studying   D.to have been studying

 I’ve worked with children before,so I know what______ in my new job.
  A.expected       B.toexpect         C.to beexpecting  D.expects 

It is said in Australia there is more land than the governmentknows______.
A.it what to do with        B.what to do it with    C.whatto do with it      D.to do what with it

Theman we followed suddenly stopped and looked as if _______ whether he was goingin the right direction.
A.seeing               B.having seen                C.to have seen  D.to see