One example of a cause-and-effect sentence is, "Because he studied more than usual for the test, Bob scored higher than he had on previous exams." Such a sentence must contain an event that happens and an explanation of what makes it happen.
In a cause-and-effect sentence, a relationship between two actions exists. One action, the effect, is the result of the other action, the cause. In the example sentence, the effect is that Bob scored higher than he had on previous exams. The cause, or reason, is that he studied more than usual for the test. Words often found in cause and effect sentences include "because," "since," "then" and "if."