Apart from Pluto, the outer planets_______ the inner planets and are made mainly of lighter materials such as

hydrogen and helium.

Of all the candidates, Peter is probably_______

_______ porpoises and dolphins, whales are mammals.

A baby might show fear of an unfamiliar adult, _______ he is likely t smile and reach our to another infant.

It is_______ that I have read it twice.

The Romans used central heating systems very much like_______.

That child behaves_______ of all

The United States spends more money on advertising_______ country in the world.

_______plants, which manufacture their own food, animals obtain nourishment by acquiring and digesting their food.

A microscope can reveal vastly_______ detail than is visible to the naked eye.

Nerve cells, or neurons, _______ in the human body.

The deep oceans contain some of the_______ of all living creatures.

The rooms in the front_______ noisier than those in the back.

_______ we finish the project, _______ we can start the next one.

The younger you are, _______ it is to learn.

This house is_______ the others we've seen.