without vs unless

[Duc]

Hello,
I saw the sentence below in my exercise book:
You won't pass the exam......studying harder.
A.unless b.without c.if d.in case.
I chose ''unless'' but the correct answer is ''without''.I don't understand it.
Could you tell me the difference between Unless and Without.
Thank you.
_________________
Don't see your shade think you are great

[Yankee]

Hi duc

A correct sentence with 'unless' would be this:
You won't pass the exam unless you study harder.

The word 'unless' is a conjunction and it joins two clauses. After 'unless' you need a subject (you) and a verb (study).

The word 'without' is a preposition in your sentence. The second half of your sentence is "... studying harder." You do not have a subject, and there is no verb tense. Instead you have the "-ing form" of a verb. Whenever you have a verb after a preposition, the verb will be in the '-ing form' (a gerund).
.