In the seventeenth century, North America was vast and unconquered, ____ only at great cost.
A. by promising riches but by yielding its bounty
B. its riches were promised but its bounty yielded
C. it promised riches but yielded its bounty
D. promising riches but yielding its bounty

Note: I have no idea what the sentence is talking about (especially what comes after “but”)… what do you think is the meaning of the sentence?
Also, shouldn’t it be “at A great cost?”

Question

In the seventeenth century, North America was vast and unconquered, ____ only at great cost.
A.	by promising riches but by yielding its bounty
B.	its riches were promised but its bounty yielded
C.	it promised riches but yielded its bounty
D.	promising riches but yielding its bounty

Note: I have no idea what the sentence is talking about (especially what comes after “but”)… what do you think is the meaning of the sentence? 
Also, shouldn’t it be “at A great cost?”

Answer

The answer is D, and no, "at great cost" is a set expression and does not require the indefinite article. The meaning is that in the 17th century, America was rich in natural resources, but to acquire these resources you had to excavate, explore, etc., and obtain them at a very high cost (probably because there was no infrastructure and modern technology, etc in 17th century America).