If Houseplants Must Be Left Unattended for a Length of Time

If houseplants must be left unattended for a length of time, some people recommend placing plastic bags over them. What is the reasoning behind this?

A) Water tension will decrease.
B) The plants won't freeze.
C) Photosynthesis will increase because of trapped carbon dioxide.
D) Transpiration will be slowed and more water will be retained in the soil.
E) The bag will trap oxygen.