If l, m, n are the direction cosines of a position vector \(\vec{a}\), then which of the following is true?

If l, m, n are the direction cosines of a position vector \(\vec{a}\),

1.	If l, m, n are the direction cosines of a position vector \(\vec{a}\), then which of the following is true?
A.	l2+m2-n2=0
B.	lmn=1
C.	l2+m2+n2=1
D.	l2 m2+n2=1
Answer» D.