Question no 12 english grammar

it is obviously no A ,mustn't

B). It tells you the order in which things happen.

Explanation:

Visualization is elucidated as one of the most commonly employed reading strategies that assists the readers to understand the text clearly and comprehensively by generating mental images of the content(provided by the author) and associating himself/herself with it.

As per the question, visualization of the series or sequence of events would turn quite helpful to the reader for better understanding the lesson(on volcanoes) as it would 'tell the the correct order of events' to him/her. Thus, the reader would be able to imagine the entire process in a systematic order that would help him/her in acknowledging the lesson inclusively and remember it for a longer time(as they have understood it actively through association). Therefore, option B is the correct answer.