Answer:
All of the above
Explanation:
Although the option isn't listed in the question, I see that you have commented that the fourth option, <em>D. All of the above</em>, exists.
The word <em>effect</em> can be both a noun and a verb. As a noun, it is often mixed up with the verb <em>to affect</em> (<em>effect vs affect</em>), but it can also be a verb meaning <em>to cause something to happen. </em>We could write the first sentence differently as: <em>The student council wants </em><em>to cause (= to effect) a change</em><em> in the dress code.</em>
<em>Effect </em>as a noun is used in the third sentence, and it means <em>a change that is a result or consequence of an action </em>(<em>Playing sports can </em><em>cause a change in (= have an effect on)</em><em> students' academic performance</em>).
In the second sentence, we have the verb <em>to</em> <em>affect</em>, which means <em>to have an effect</em> (<em>Receiving a good grade will </em><em>have an effect on (= affect)</em><em> the student's motivation). </em>