<p>Which mean I can take it in whichever quarter when it is?</p>
<p>Basically "Economics 10" course is split into two quarter courses: Economics 10A and 10B. Correct?</p>
<p>If Econ 10B existed (it does not: there is Econ 100B, which follows Econ 10A), then it would be the second in a sequence of courses. Each enumerated course is its own course, to be completed in one quarter. For example, Chem 1A, 1B, and 1C are each discrete courses. You can enroll in each in whichever quarter you have met the prerequisites and the course is offered.</p>