>>> C = np.array([123,188,190,99,77,88,100])
>>> A = np.array([4,7,2,8,6,9,5])
>>> A<=5
array([ True, False, True, False, False, False, True], dtype=bool)
Returning all the elements of C, where the corresponding value in A is less or equal than 5:
>>> C[A<=5]
array([123, 190, 100])
>>> B=A<=5
>>> C[B]
array([123, 190, 100])