Correct Answer: Efforts to control the invasion of locusts in Rajasthan and Gujarat have been stepped up by the authorities.

Solution : The correct choice is the fourth option.

Passive voice involves rearranging the structure of a sentence so that the subject receives the action of the verb rather than performing the action itself. In this case, "efforts" (the subject) is the recipient of the action "stepped up", which is performed by "the authorities".

The structure of passive voice sentences is: object + "to be" verb + past participle + by + subject (optional).

Therefore, the correct answer is: Efforts to control the invasion of locusts in Rajasthan and Gujarat have been stepped up by the authorities.