Which of the Following Occur(s) When Water Vapor Is Added

Multiple Choice

Which of the following occur(s) when water vapor is added to a dry gas at a constant pressure?
1) The volume occupied by the gas mixture decreases.
2) The relative humidity of the mixture increases.
3) The partial pressure of the original gas is reduced.

A) 1 and 2 only
B) 1 and 3 only
C) 1, 2 and 3
D) 3 only