The word "labor" is roughly synonymous with "work" - and especially hard work, or physical work.
"Salary" is compensation for work- but not work itself.
Work is also not a reference, but far from it.
Work, however, is a human resource - and so it labour. The last option is the correct one!
Answer:
True
Explanation:
Thus, an aquarium is self-perpetuating functional unit. Therefore, it is known as ecosystem. Since the fishes and plants and others are added by man, so it is known as artificial ecosystem. What are trophic levels?
rocks are used for making carvings sculpture
rocks consist useful minerals like gold silver
soil is formed by disintegration of rocks
rock salt is found in rocks which is used for freezing and cooking