certain elementary reaction, A + B → Products, it was determined that a reaction occurs every time that the two reactant molecules collide.?

A is false.
Bond formation is exothermic, and thus the enthalpy change for the reaction is negative.

B is true.
This is because the reaction occurs every time when the two reactant molecules collide no matter what the orientation is.

C is true.
As the reaction is a single-step, the rate-determining step is
A + B → Products
The order of reaction is determined by the rate-determining step, i.e. Rate = k[A][B]

D is true.
This is because the reaction occurs for every collision of the two reactant molecules.

The answer: A. The enthalpy for the reaction must be positive.

B