What action does an investor take when making a long margin purchase of common shares...

A long margin purchase means buying securities partly with borrowed funds from the dealer .

The investor pays part of the purchase price (the margin), while the dealer lends the balance .

This differs from:

A (cash purchase): uses only own funds.

B (limit order): unrelated, based on price conditions.

D (short sale): selling borrowed shares, not buying.

Correct action = buying shares on borrowed funds at market price.