Answer: It could be Islam.
Step-by-step explanation:
Usually, when the phrase "religion of peace" is said, the conversation is always around Islam. Peace is greatly associated with Islam. Even when Muslims greet each other, they say "asalamu alaykom," which means "peace be upon you."
As for the dressing plainly portion, Muslims are supposed to dress modestly. This means that they are supposed to avoid tight or revealing clothing.