How many orbitals have the quantum numbers :

$n=4,\mathit{ }l=3, m_l=0$?

There are 7 orbitals for $n=4,\mathit{ }l=3, m_l=0$.

The total number of orbitals in a particular subshell depends on the orbital's "l" value. 
The equation (2l + 1) provides the answer. . There can be two electrons in each orbital.
As an example, the (n=4, l=3) has 7 orbitals 
The no of orbital in subshell is found by the formula,
l= 2l +1 
l=(2*3 + 1)
l=7

Hence, the option A is correct.