3 Polystyrene foam is less dense than water. Molly measured the volume of a small block of foam by submerging it in water in a measuring cylinder.
The pictures show her results.
Forces in action
cm3
240
-220
cm3
240
220
200
180
160
140
-120
100
cm3
240
-220
-200
-180
160
140
120
100
80
60
200
180
160
140
120
100
80
60
water
80
160
40
20
steel
40
20
40
20
polystyrene

The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs. 

answer: you could do some invislibe ink.

explanation: i will tell you how to if u answer my question.

i'm assuming that the correct answer is indeed the first one/ "a"..