Explanation:
"Function of a reservoir in a nutrient cycle is to meet the deficit which occurs due to imbalance in the rate of influx & efflux. Give an account of energy flow in an ecosystem."
Arthropods were the first animals to successfully invade land from the sea
CH3- methyl group
COOH- carboxyl group
H2O- just water
NH2- amino goup
OH- hydroxyl group
the answer is H2O