In the question given below, a part of the sentence is in bold and italicised. Below are given alternatives to the bold and italicised part which may improve the sentence. Choose the correct alternative. In case no improvement is needed, choose option 'D' as the answer.
Not long back, in Japan, a mysterious nerve gas affected a large number of people.
effected
infected
infested
No improvement
Correct answer is B
No explanation has been provided for this answer.