The most logical thing to do is use a file with a list of questions and their associated answers on each line. You could also use an XML file or SQLlite which is built into PHP 5.

Example text file format:
Code:
1||Question 1||C||Option A, Option B, Option C
2||Question 2||B||Option A, Option B, Option C
3||Question 3||A||Option A, Option B, Option C
Example XML file format:
Code:
<questions>
    <question id="1">
        <text>Question 1</text>
        <answer>C</answer>
        <options>
            <option id="A">Option 1</option>
            <option id="B">Option 2</option>
            <option id="C">Option 3</option>
        </options>
    </question>

    <question id="2">
        <text>Question 2</text>
        <answer>B</answer>
        <options>
            <option id="A">Option 1</option>
            <option id="B">Option 2</option>
            <option id="C">Option 3</option>
        </options>
    </question>

    <question id="3">
        <text>Question 3</text>
        <answer>A</answer>
        <options>
            <option id="A">Option 1</option>
            <option id="B">Option 2</option>
            <option id="C">Option 3</option>
        </options>
    </question>
</questions>