A serious study of physics is impossible _______ some knowledge of mathematics．
A．againstB．before
C．beyondD．without
It was only after he had read the papers _______ Mr．Gross realized the task before him was extremely difficult to complete．
A．whenB．thatC．whichD．what
It may not be a great suggestion．But before _______ is put forward, we’ll make do with it．
A．a good oneB．a better one
C．the best oneD．a best one
The watch was very good, and he _______ 20 percent down for it．
A．paidB．costC．boughtD．spent
We _______ very early so we packed the night before．
A．leaveB．had left
C．were leavingD．have left
Since nobody gave him any help, he ______ have done the research on his own．
A．canB．mustC．wouldD．need
