If a significant fraction of heavy components is present in the natural gas mixture， laboratory measurements of（） of the C7+ fraction are required to use mixing rules.

If a significant fraction of heavy components is present in the natural gas mixture， laboratory measurements of（） of the C7+ fraction are required to use mixing rules.
A.the molecular weight
B.mole fraction
C.gravity
D.critical temperature
E.critical pressure
正确答案：the molecular weight；mole fraction；gravity