One of California's greatest problems is providing adequate water to meet the needs of its expanding population.

A．He runs.
B．He invented the clockwork radio.
C．He was once an entertainer.
D．He runs a company.

A．Computer may cause health problems for its users.
B．Computer has led to a revolution in every aspect of people’s life.
C．Computer is financially within the reach for most consumers.
D．The influence of computer has on people’s life is not as great as people have predicted.