It is easy for boats to tumble over in the Colorado River because ______.

A．Light speed is millions of times faster than sound speed.
B．Light speed is a million times slower than sound speed.
C．Light speed is about millions of times faster than sound speed.
D．Light speed is about a million times faster than sound speed.

A．The lack of a qualified sales force.
B．Lower price in suburban shopping malls.
C．Unpleasant highway commuting.
D．Limited land available.