. . . . . . . you do not work you cannot succeed.

The correct answer is: Unless.

• If is used to introduce a condition that is necessary for something to happen. For example, “If you study hard, you will pass the test.”
• Unless is used to introduce a condition that is necessary to avoid something happening. For example, “Unless you study hard, you will fail the test.”
• Till and until are both used to introduce a point in time up to which something happens. For example, “I will wait here till you come back.” or “I will wait here until you come back.”

In the given sentence, the speaker is saying that you cannot succeed unless you work. This means that working is a necessary condition for success. If you do not work, you will not succeed.