Dust storms most often occur in areas where the ground has little vegetation to protect（）of the wind.

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

A．delayed
B．adjourned
C．cancelled
D．preserved

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