Vietnam has a tropical monsoon climate. during the rainy season warm air comes in from the north and rises, allowing cooler air and rain clouds to move in. where does the warm air most likely come from?

The warm air that comes in Vietnam during the rainy season is most likely from the Pacific Ocean. In fact, tropical storms that pass over Vietnam form over the Pacific Ocean when the water warms up. The Pacific Ocean is at its warmest from June to November and the warm air and typhoons move inland over Vietnam. 

A,b,c is the answer to the question

The answer would be  b. hope this !