Final answer:
In an uncontrolled intersection, the driver on the left must yield the right of way to the driver on the right, thus (a) is the correct answer.
Step-by-step explanation:
When two vehicles enter an uncontrolled intersection, the general rule is that the driver on the left should yield the right of way to the driver on the right. This means that the correct answer is (a) driver on the right.
This rule is applied to ensure safety and order on the roads when traffic signals or signs do not govern the right of way. However, it's important to always approach an intersection with caution and be prepared to yield if it helps prevent an accident. Furthermore, if the intersection is congested or if there are other specific local traffic rules, those will take precedence over the general rule.