What type of phrase or clause is “was attending”

The correct answer is: the verb phrase.

Explanation:

The verb phrase consists of a main verb alone, or the main verb + any auxiliary or modal verbs.  

In this case, the verb phrase was attending has a continuous meaning. It's a syntactic unit composed of at least one verb and its dependents (objects, complements and other modifiers), and not always includes the subject.

The verb phrase is similar to what is considered a predicate.

either a donut or a sphere or a pancake or a flat sphere. it depends on where the vertical line is.

if the line goes through the center of the circle and is perpendicular to a diameter containing the center, then you get a flat circle.

if the line and the diameter of a the circle meet in the center of the diameter and at an angle, you get a pancake.

if the line is on the circumference of the circle and is at right angles   to the circle you get a ring.

if the line contains the diameter, you get a sphere.

the the line is parallel to the diameter and touches the circumference, you get a donut.