If $$n$$ is a multiple of $$7$$ and $$n=s^2t$$，where $$s$$ and $$t$$ are each prime numbers, which of the following expressions must be a multiple of $$49$$？
If $$n$$ is a multiple of $$7$$ and $$n=s^2t$$，where $$s$$ and $$t$$ are each prime numbers, which of the following expressions must be a multiple of $$49$$？
