Q1: What circuit activity may shift a characteristic curve so that diode operating points are different?

ANS:A - higher power (heat)

The total value of collector current is given by collector current+reverse saturation current. For every 10 degree raise in temp the reverse saturation current doubles thereby increasing the collector current. As the collector current increases the diode operating point shifts towards breakdown region which in turn increases the temperature and continuing the above process (early effect).