Crate A is in contact with identical crate B on a frictionless horizontal floor. A person pulls crate B to the right with a rope, so the two crates accelerate together. Consider the horizontal force of crate A pushing on crate B. Which of the following forces is the action–reaction partner of that force?
a) The tension force of the rope pulling on crate B
b) The horizontal force of crate B pushing on crate A
c) The horizontal force of the floor pushing on crate B
d) The horizontal force of crate A pushing on crate B