'Good' is an adjective which can describe the noun, 'habit' but not the gerund, 'reading'. Hence, the phrase 'good habit' is acceptable. But, 'good reading' is not an acceptable or meaningful phrase. Hence, the
sequences in options A and D do not make meaningful sentences. Options A and D are incorrect. Option B: The full stop at the end of the sentence indicates this is an assertive sentence. An assertive sentence does not usually start with the word 'Is'; Only interrogative sentences start with 'Is'. Hence, this option is incorrect.
Option C: This sequence follows the subject-verb pattern. 'Reading' is the subject. The verb is 'is. 'Good habit' is the predicate. The sentence is meaningful. Option C is correct.