The dense Belgian fogs is caused by the cooling of humid surface air to a relatively low temperature（）.

单项选择题The average age at which people begin to need eyeglasses vary considerably（）.

A．varies
B．is varied
C．will vary
D．has been varied

单项选择题The voters were overwhelmingly against the candidate his proposals called for higher taxes（）.

A．who
B．whose
C．whom
D．which