Parallel Structures

Great quantities of water circulate either temporarily ________ in a concentrated flow of streams and rivers.

• and permanent

• and permanently

• or permanent

• or permanently

Astronauts are expected to be capable of operating at peak efficiency in outer space in both normal _________ emergency situations.

• nor

• and

• or

• but also

An astronomical observatory is a station--either a building _________ a group of building--used for the study of the heavens.

• or

• and

• but also

• nor

In commensalism, tiny plants live out their lives in the human body and derive their food from it, but probably neither harm nor _______ the host in any way.

• to help

• helping

• helped

• help

Plants require both large amounts of carbon, oxygen and hydrogen ____ smaller quantities of phosphorus, potassium and calcium.

• and

• or

• nor

• but also