Which statements regarding margin buying and short selling are correct?

When brokers increase the initial margin, investors would need to put in less

cash to open the account.

Short$-$selling investors have the potential to experience unlimited loss.

When brokers increase the maintenance margin, investors would receive margin

calls later.

When brokers increase the initial margin, investors' leverage effect would be

smaller.

The leverage effect in margin buying and short selling could multiply the return

and minimize the risk.