题目内容：

I watched him _____ he disappeared from the sight in the distance.
A.Since
B.After
C.Until
D.Because
_____ I admit that problems are difficult ,I do not agree that they can not be solve.
A.While
B.Suppose
C.Because
D.Until
这两道题一点思路都没有,奇奇怪怪的,请高人指教,