The correct answer is option C: restricted sales primarily to speculators.
Step-by-step explanation
Congress's land policy of selling sections of 640 acres at a dollar an acre previous to 1800 was helpful because it mainly restricted sales to speculators.
Speculators or land speculators, in this case, are people who buy land expecting that it will increase its value to sell it to a higher price. That is to say, they buy land and keep it until it they can take a profit from it.