Which of the following is a molecular compound? O3, CH4, NaBH4, CaC2

a). you know from previous experience that steaming things are hot,
so you infer that this one will also be.

b). you know from previous experience that rain often happens after you see
dark clouds in the sky, so you infer that it will also happen this time.

c). when two chemicals are mixed together, you observe bubbles forming.

d). from previous experience seeing plastic bags moving along the ground
on a windy day, you infer that the wind is the cause of their behavior.