There/ be/two/ boys/class/ tall/work/ monitor/.
A.There are two boys in my class the tallest of whom works as the monitor.
B.There are two boys in my class, the taller of whom works as the monitor.
C.There are two boys in my class, the tallest of them works as the monitor.
D.There are two boys in my class, the taller of them works as the monitor.