1) The amount of water on Earth is  
a. always the same.
b. constantly changing
c. steadily increasing.
d. steadily decreasing.

2) What controls whether water is a gas, liquid or solid ice?

a. the shape or size of the cup
b. where it has been stored
c. if it is being used for irrigation
d. what its temperature is​

1. in which sentence is the underlined portion a predicate nominative? for astronauts, going into space to repair orbiting equipment becomes a challenge. for astronauts, going into space to repair orbiting equipment becomes tricky. for astronauts, going into space to repair orbiting equipment becomes challenging. for astronauts, going into space to repair orbiting equipment becomes frequent.