Answer
"Since the weather was so hot, many people decided to go to the beach to cool off."
Step-by-step explanation:
In this sentence, the cause is the hot weather, and the effect is people going to the beach to cool off. The transition word "since" indicates the cause-and-effect relationship between the two clauses. Other common transition words that can be used to indicate cause and effect include "because," "as a result," "due to," and "hence."