driving old cars often can be expensive.
which error does the sentence above make?
a)misplaced modifier
b)dangling modifier
c)squinting modifier
d)fragment

The error that this sentence makes is C. squinting modifier.
A squinting modifier is usually an adverb which makes a sentence somewhat unclear by changing the meaning of the words before or after it. So here, we aren't exactly sure whether the adverb often refers to driving cars often or the fact that driving cars can be expensive often.