塑料是由什么制成的？

What are plastics made of?

这条裙子是由什么制成的？

What's the skirt made of?

但是你知道胸罩是由什么制成的吗？

I need you to take off your bra too.

但是你知道胸罩是由什么制成的吗？

But do you know what is bra made of?

第二，我们根本不知道身边各种产品是由什么制成的。

And the second, is that we actually don't have a clue of what all these products that surround us are made of.