question:
The ratio of an object's mass to its volume is its

answer:
density.

question:
Lemon juice turns litmus paper red, is corrosive and tastes sour. Lemon juice is classified as

answer:
an acid.

question:
What can a moving magnet in a coil of copper wire cause?

answer:
an electric current

question:
Why should plants be included in investigations about the water cycle?

answer:
Plants are part of the water cycle through the process of transpiration.