《中华人民共和国航行资料汇编》是（）。

Airmasses are classified according to the regions where they originate. They are generally divided into polar or tropical to identify （ ） characteristics.

Which of the following is not a general weather characteristic associated with cold fronts?

When flight speed is constant, the greater the air density,

A warm front is one where （ ） ．

A cold front is one where （ ） ．

When judging the wing speed by wind sock, if the wind sock is at aclinic level, then the wind speed can be up to（ ）m/s.

（ ） cannot be an indication to the passage of a frontal system.

When the A/C flies from one airmass into another, an airmass with different（ ）properties may be expected.

The boundary between airmasses is called a （ ） ．

An air mass is a body of air that （ ） ．