There are 50 students admitted to a nursery class. Some students can speak only English and some can speak only Hindi. Ten students can speak both English and Hindi. If the number of students who can speak English is 21, then how many students can speak Hindi, how many can speak only Hindi and how many can speak only English? (a) 21, 11 and 29 respectively     (b) 28, 18 and 22 respectively (c) 37, 27 and 13 respectively     (d) 39, 29 and 11 respectively