Drop that variable: The following MINITAB output presents a multiple regression equation

It is desired to drop one of the explanatory variables. Which of the following is the most appropriate action?
i. Drop x1, then see whether R2 increases.
ii. Drop x2, then see whether adjusted R2 increases.
iii. Drop x4, then see whether R2 increases.
iv. Drop x1, then see whether adjusted R2 increases.

= b + bx + bx+b3x3 + b4x4-