alimad
3. Many writers of modern English have acquired careless habits that damage the clarity of their prose,
but these habits can be broken if they are willing to take the necessary trouble.
(A) but these habits can be broken
(B) but these habits are breakable
(C) but they can break these habits
(D) which can be broken
(E) except that can be broken
C is the best candidate.
Many writers (plural) have acquired habits....but
they can break these habits....
According to some previous posts there is ambiguity in
they.
but
they can break these habits
Now
they cannot refer to habits as habits cannot break habits so the only other possibility is they refer to Writers.
Now in the remaining portion:
if
they are willing to take the necessary trouble.
Here also they can refer to writers only.
As there is no ambiguity sentence construction seems reasonable. However the better construction would have been:
Many writers of modern English have acquired careless habits that damage the clarity of their prose, but the writers can break these habits if these writers are willing to take the necessary trouble.I hope it makes sense now.