I'd say the answer is D. Hope this helps :)
<span>Isohalines are lines (or contours) that join points of equal salinity in an aquatic system.</span>
<span>Kalpakkam is in A. Tamil Nadu. Which is located in South India :)
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Nevertheless, the unifying influence of the monsoons on the Indian subcontinent is quite perceptible. ... These monsoon winds bind the whole country by providing water to set the agricultural activities. Thus, in view of the above the monsoon is considered as a unifying bond for this subcontinent.
