Ocean basin size and continental margins
a. Ocean basins change size over long periods.
b. The type of tectonic activity is an important reason for this.
c. Oceans expand where new crust is being formed by tectonic activity.
d. Oceans shrink where crust is destroyed by a different type of tectonic activity.

Option (A)

Explanation:

Ocean basin covers a large amount of area on the earth's surface. They have been constantly changing over a long period of time in terms of both shape as well as size.

The size of the ocean basin is controlled by the rate of subduction and rate of spreading that is going on since the geological time. High spreading rate leads to the increasing size of the ocean basin, whereas high rate of subduction decreases the size of the ocean basin.

Thus, the correct answer is option (A).