As the chairman is ill, I am asking Mr. Sharp to act ______ him.

A．for a moment
B．in a moment
C．the moment
D．at the moment

A．If clouds are high, there will be bad weather.
B．The color of clouds is a factor to help predict the weather.
C．If the weather is good, the clouds must be very low.
D．To study clouds is the only way to understand the weather.