Answer:
a. evaporation .
Step-by-step explanation:
In this case, given the described situation, we should take into account that there are two types of liquid-gas phase transitions, evaporation and vaporization, which occur in totally different way.
Firstly, evaporation is a superficial phenomena, it means that it occurs at the surface of the liquid only whereas the vaporization is a bulk phenomena, which means that it occurs along the whole volume of liquid.
In such a way, we can infer that cold steam stream flowing over the pond has the capacity to strip or remove liquid water molecules in the pond and take them to the vapor phase, which means that the answer is a. evaporation .
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