— I think that this is an interesting lecture _____.
— Oh, come on! No lectures for me. I've been tired ____ to lectures.
A:to listen to; of listening
B:to listen; of listening
C:to listen to; to listen
D:to listen; to listen
____
如图所示,R1为定值电阻,R2为负温度系数的热敏电阻,L为小灯泡,当温度降低时( )