The correct answer is: B. are flown
Kites are flown by children, adults, girls and boys in India.
The verb “fly” can be used intransitively (without an object) to mean “to move through the air by flapping wings” or “to travel through the air in a vehicle”. It can also be used transitively (with an object) to mean “to cause (something) to move through the air by flapping wings” or “to cause (something) to travel through the air in a vehicle”.
In the sentence “Kites are flown by children, adults, girls and boys in India”, the verb “fly” is being used transitively. The object of the verb is “kites”. The sentence means that children, adults, girls and boys in India cause kites to move through the air.
The other options are incorrect because they do not agree with the subject of the sentence. The subject of the sentence is “kites”, which is plural. Therefore, the verb must also be plural. The options “A. flying”, “C. are fly” and “D. flew” are all singular.