The incident at school precipitated the need for more security. A. lessened B. oppressed C. happened after D. brought about

the answer is d.

Explanation:

The incident at school precipitated the need for more security. In this sentence, the word precipitated means: brought about.

D. brought about

Explanation:

The word precipitate refers to making something to happen suddendly or sooner that expected.

In this case something happen at a school which had a sudden consecuence or reaction, the need for more security became a priority.

The phrasal verb to bring about is the one that is closer to that meaning as it means to make something happen making changes in the situation.