When we put the suggestion to him, he thought highly of it and was ______ about its immediate application.

A．curious

B．content

C．cautious

D．enthusiastic

如图所示，某同学将空的薄金属筒开口向下压入水中。设水温均匀且恒定，筒内空气无泄漏，不计气体分子间的相互作用，则被淹没的金属筒在缓慢下降过程中，筒内空气体积减小

 [ ]

A．从外界吸热

B．内能增大

C．向外界放热

D．内能减小