In the following passage some words have been deleted. Fill in the blanks with the help of the alternatives given. Select the most appropriate option for each blank.

The locust is an insect that belongs to the family of grasshoppers. These insects are essentially harmless (1)
________they meet certain circumstances under which they (2)________ more abundant and change their behaviour. India, Pakistan and Iran (3)________ currently thinking over the locust plague threat (4)________ over their economies. When these locusts meet (5)________ environmental conditions, they become gregarious and (6)________ breeding abundantly. With their population becoming (7)________, they form swarms and keep moving (8)________ areas damaging the crops. These swarms attacking (9)________ and thereby devastating the entire agricultural economy is (10)________ is commonly referred to as locust plague.