The rich merchant not only rewarded the honest woman with money, but also gave her a job.
The conjunction, 'Not only.. but also' is called a correlative conjunction which combines two grammatically equal items. This means that the words following both parts (i.e 'not only' as well as 'but also') should belong to the same parts of speech. Using different parts of the speech after 'not only' and 'but also' makes the sentence imbalanced and grammatically incorrect.
Option A: 'Not only' is followed by 'the honest woman' which is a noun phrase. However, 'but also' is followed by 'gave her a job' i.e verb+object. Hence, this option is grammatically incorrect.
Option B: When a sentence begins with 'not only, it is followed by an auxiliary verb like 'did' or 'does' + subject. Example: 'Not only did the rich merchant reward the honest woman' is the correct usage. In this option, the sentence begins with 'Not Only'. However, there is no auxiliary verb which immediately follows. Hence, this option is incorrect.
Option C: The words, 'not only' is followed by the verb 'rewarded. The words, 'but also' is also followed by a verb, 'gave'. Hence, this option is correct.
Option D: In this option, the words, 'but also' are separated. Hence, this option is incorrect.