Currents ________ __________ by differences in temperature, salt content, and wind.

• are caused

• are cause

• were causing

• have been cause

Because of the way they move, currents _________ _____________ rivers under the ocean.

• were consider

• are considering

• are considered

• are considerren

Many floods and droughts in the world ______ _________ _______ by the El Niño and La Niña currents.

• were being caused

• have been caused

• are caused causing

• has been caused

High tide is caused because water ______ ___________ to the moon.

• was atracting

• is attracting

• is attracted

• is attractive

Water from the oceans ____ __________ because of the attraction between the moon and earth, which produces tides.

• is moved

• is moving

• was moving

• is move

Tides _____ ______ ________ at the beach because the coast grows wider or narrower according to the sea level.

• are being saw

• can be saw

• can be seen

• is been seen

More light _______ ________________ (receive - present) in the photic zone than the aphotic zone.

A lake _____ __________ into three zones: the littoral zone, the limnetic zone, and the profundal zone. (divide - present)

During photosynthesis, water and carbon dioxide _____ ________ to make food for plants. (use - present)

The aphotic zone _______ ___________ by animals such as the octopus and the squid, which are able to swim up closer to the surface to find food. (inhabit - present)