目的地拉力也叫市场吸引力，它与旅游需求量的大小成（）变化。

A.正方向

B.反方向

C.螺旋型

D.无规律

I guess we've already talked about this before but I'll ask you again just _____.[ ]

A. by nature  

B. in return

C. in case  

D. by chance