If you want to change yourself from a pessimist into an optimist, the first thing you should do is ______ to your thoughts when bad things happen.

A．Crimes committed by young people.
B．Crimes committed by needy people.
C．Influence on young people.
D．Stealing and violence.

A．He has a cold.
B．He has the flu.
C．He has a stomachache.
D．He has a toothache.