Question

unless you run fast, you will not catch the train (use: if)​

Answer 1

If you wouldn't run fast, you will not catch the train

Answer 2

If you run fast, you will catch the train.

The word that has been asked to use while rewriting the provided sentence is a conjunction.

• A conjunction joins two or more sentences.
• Words like and, but, or, so, because, though, although, therefore, both...and, not only... but also, etc., are conjunctions.

In the above sentence, 'if' is the conjunction.

• These words are used to join two or more sentences.
• These words make sentences simpler and easier to understand.
• Conjunctions do not change the intended meaning in any way.