D.
first increases then decreases
✓
D.
first decreases then increases
✓
B.
A is perpendicular to B
✓
A.
10 N along the x-axis
✓
B.
8 N along the x-axis
✓
C.
6 N along the y-axis
✓
A.
B must be a null vector
✓
B.
A and B must be perpendicular
✓
C.
A must be a null vector
✓
D.
A and B must be parallel
✓
