Today’s scientists have overcome many of the challenges of the depth by ________ more sophisticated tools.

A big ocean in the world is divided ___________ five different parts: the Pacific, Atlantic, Indian, Antarctic and Arctic Oceans.

Oceans altogether cover 75 __________ of our Earth.

They can send submarines to take photographs of animal life and bring back to the __________ for further study.

Organisms play ________ important role in keeping the nature balanced.

Is submarine a ___________ of transport in your country?

A large number of jellyfish are _________ stake due to overhunting.

The director _______ for the meeting by the time I got to his office. 

This season's _______ include five new plays and several concerts of Chinese and Indian music.

I _________ smoking should be banned, especially in restaurants.

I love learning about _________ life under the sea.

We wish _______ to college next year. 

My mother told me she _______ very tired since she came back from a visit to our grandparents.

They will never forget _______ the man-eating shark at the beach.

What should we do ____________ biodiversity?