Mr Philip has made ______ survey on students’ lunchtime, and ______ survey shows us a lot of problems.
A:an; an
B:the; the
C:a; the
D:the; a
猜想一:滑动摩擦力的大小与压力的大小有关
猜想二:滑动摩擦力的大小与物体间接触面的粗糙程度有关
猜想三:滑动摩擦力的大小与物体间的接触面积大小有关