----In recent years, _____problem of global warming has become very serious.

----That’s right. People are facing _____diversity of natural disasters now.

A．/, a

B．a, the

C．the, a

D．a, a

如图甲、乙和丙是我们做过的一些实验．图甲中小磁针发生偏转，说明通电导体周围存在______；图乙中用导线触接电池时，收音机发出喀喀声，说明了______的存在；图丙中水蒸气将塞子弹出，说明了通过______方式可以改变物体内能．