Correct Answer: Wane

Solution : The correct choice is the fourth option.

Wax means to become larger or stronger whereas wane means to progressively become smaller.

The meanings of the other options are as follows:

• Polish: It refers to the process of making something smooth and shiny.

• Cane: It refers to a type of plant or a walking stick.

• Wail: It means to make a loud, mournful cry.