全文是:SAM:Is that bag heavy, Penny?
PENNY:Not very.
SAM:Here! Put it on this chair. What’s in it?
PENNY:A piece of cheese.
A loaf of bread.
A bar of soap.
A bar of chocolate.
A bottle of milk.
A pound of sugar.
Half a pound of coffee.
A quarter of a pound of tea.
And a tin of tobacco.
SAM:Is that tin of tobacco for me?
PENNY:Well, it’s certainly not for me!
请问penny的书包里有这么多东西,为什么用What’s in it,而不用复数形式What’re in it?