A conditional sentence has 2 parts, the condition and the consequence:
If you study, you will pass your exam.
Here, the condition is STUDY, shown by the word IF, and the consequence is PASS YOUR EXAM.
There are several types of conditional sentences, but our interest here is how they are tested in the FCE sentence transformations:
There is a connection between the words IF, UNLESS and BECAUSE.
IF you study, you will pass your exam.
You will not pass your exam UNLESS you study.
You will pass your exam BECAUSE you studied.