ALTSM 22/03 Q91

The answer is D) 30^o,45^o
We know that for a vector, cos²a + cos²b + cos²c = 1 , (where a,b,c are the angles made by the vector from                                                                                          positive x,y,z axis resp.)
or cos²a + cos²b = sin²c
Now, 0 ²c ²a + cos²b
This condition is followed by every given set except the D) one.
Hence, that is your answer.