Identify the Set of Four Quantum Numbers That Could Represent $\frac{1}{2}$

Multiple Choice

Identify the set of four quantum numbers that could represent the last electron added (using the aufbau principle) to the Sr atom.

A) n = 5,l = 0,m_l = 0,m_s = - $\frac{1}{2}$
B) n = 4,l = 1,m_l = 1,m_s = - $\frac{1}{2}$
C) n = 5,l = 1,m_l = 0,m_s = + $\frac{1}{2}$
D) n = 4,l = 1,m_l = -1,m_s = + $\frac{1}{2}$
E) n = 5,l = 1,m_l =1 ,m_s = - $\frac{1}{2}$