Our flight to Guangzhou was（）by a bad fog and we had to stay much longer in the hotel than we had expected.

单项选择题We have had to raise the prices of our products because of the increase in the cost of（）materials.

A．primitive
B．rough
C．original
D．raw

单项选择题Hydroponics（）the cultivation of plants without soil.

A．does
B．is
C．do
D．are