Which is true? a)the spin angular momentum vector itself can be measured, and it can be aligned along the measurement axis (z axis).b)the spin angular momentum vector itself cannot be measured, but its component along the measurement axis (z axis) can be measured. c)the spin angular momentum vector itself can be measured, and its component along the measurement axis (z axis) can also be measured. d)the spin angular momentum vector itself cannot be measured, but it can be aligned along the measurement axis (z axis).