The vertical pair of forces.

• A. Gravity and Support
• B. Friction and Drag
• C. Buoyancy and Gravity
• D. Thrust and Drag

Answer: (A)

The vertical forces on a resting object on a surface are gravity pulling downward and the surface pushing upward (the normal or support force). They form a vertical pair because they act along the same vertical line in opposite directions. When the object isn’t accelerating up or down, these two forces balance in size, so there’s no net vertical force. The other options don’t describe this up-and-down pairing for a resting object: friction and drag act along the surface or opposite the motion, not as a balanced vertical pair; buoyancy and gravity are a vertical pair in fluids, not the usual surface case; thrust and drag relate to motion along or against the direction of travel and aren’t the standard vertical balance for a resting object.