A mercurial barometer at sea is subject to rapid variations in height (pumping) due to the pitch and roll of the vessel. To avoid this error，measurements of atmospheric pressure at sea are usually measured with a(n)（）.

单项选择题A low，uniform layer of cloud resembling fog，but not resting on the ground，is called（）.

A.cumulus
B.nimbus
C.stratus
D.cirrus

单项选择题A local wind which occurs during the daytime and is caused by the different rates of warming of land and water is a（）.

A.foehn
B.chinook
C.land breeze
D.sea breeze

单项选择题A line on a weather chart connecting places which have the same barometric pressure is called an（）.

A.isotherm
B.isallobar
C.isobar
D.isotope

单项选择题A feature of an inflatable raft which helps keep people stationary in rough weather is（）.

A.lashings on the floor of the raft for the passenger's feet
B.straps from the overhead
C.lifelines on the inside of the raft
D.ridges in the floor of the raft

单项选择题A cold front moving in from the northwest can produce（）.

A.thunderstorms，hail，and then rapid clearing
B.increasing cloud cover lasting for several days
C.lengthy wet weather
D.low ceilings with thick cirrus clouds