Answer:
Option D, grass they eat and water they drink
Step-by-step explanation:
Most of the grazing animals including buffaloes, cows, and sheep have high level of lead and zinc in their blood or milk only when -
a) They graze is any farmland or grass land which is near to any lead/zinc smelter or factories that uses these two chemicals.
b) Or when these animals drink water from water bodies contaminated by lead or zinc released by industries.
Hence, option D is correct.