单项选择题 A microbarograph is a precision instrument that provides a（）.

单项选择题 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（）.