I don't know the word. Let me ________.

Tom went back _________ yesterday again.

Let's study ________ next.

--What do you think of these two books?

--________ of them are interesting. And I've read them several times.

--Will you please show me how to operate the new machine?

--Sure. It's a piece of cake. Now let me tell you ________ to do first.

The children ________ not to play with the fire.

The population of China ________ about 1.4 billion.

There is ________ milk in the bottle. Can you get some?

Would you like ________ some fruit for lunch?

The population in developing countries ________ fast now.