All the employees agreed that the new regulations had __________ positive changes in the workplace.

Brought on— means to cause something unpleasant, usually illness or stress ("the cold weather brought on his asthma"). Pairing it with "positive changes" clashes with its negative connotation. Fails.

Brought along — means to physically bring someone or something with you ("she brought along her camera"). Regulations can't carry changes with them. Fails.

Brought up — means to raise a topic or raise a child ("he brought up the budget issue"). Regulations didn't mention changes; they caused them. Fails.

Brought about — means to cause or make something happen, and it's the standard collocation with "change": "bring about change" is practically a fixed phrase in English. So: "the new regulations had brought about positive changes in the workplace."

The sentence structure also helps confirm it — "had + past participle" with "changes" as a direct object needs a phrasal verb meaning cause, and "bring about" is the only one of the four with that meaning.

Answer: Option 1