Manufacturers rate batteries in watt-hours; if they rate the watt-hour higher, the longer the battery can be expected to last.
(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. The question can be accessed at GMAT Club)
The main idea to be communicated here is that if a battery is rated higher, it is can expected to last longer. We need to find the best way to express this idea.
The error in the given sentence is that the structure of the “if clause” and of the “then clause” don’t match. One correct way could have been “if they rate the watt-hour higher, the battery can be expected to last longer.” However, the structure in the correct option i.e. option C would still be far better than this structure in terms of structure and meaning.
(A) Incorrect. For the error mentioned above.
(B) Incorrect. Here “rating” is a verb-ing modifier modifying “it”, which is not referring to anything! The overall structure is non-sensical.
(C) Correct. The structure is clear, concise, and idiomatic and the meaning communicated is logical.
(D) Incorrect. The structure “the higher…” followed by a clause “it is that much…” is incorrect. Also, “it is that much longer that” is overly wordy.
(E) Incorrect. The structure “when the watt-hour…” i.e. a clause followed by “the longer it is…” is incorrect. Together with the non-underlined part, this option becomes “…the longer it is the battery can be expected to last”. As can be seen, the last part seems to have two subjects and two verbs!