Tom with his classmates---an English lesson now.A .has B.hav

D.is having --> Tom with his classmates [is having] an English lesson now.
Tom = subject SO is = correct!
虽然这句话看起来很奇怪,因为“with his classmates”是不着村后不着,BUT "is having" 是正确的
Because "with his classmates" CAN MOVE to anywhere:
Tom is having an English lesson [with his classmates] now.
[With his classmates],Tom is having an English lesson now.