What does the present perfect tense show?
a) action that began in the past and continues in the present
b) action that begins and ends in the present
c) action that begins in the present and continues into the future
d) future action that began in the past, extends to the present, and continues into the future.

The present perfect tense shows

(A) action that began in the past and continues in the present.

It cannot be associated with specific words that relate to time, but is rather a general expression.

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.

it is the background information on the characters and setting explained at the beginning of the story. the exposition will often have information about events that happened before the story began. the exposition is often the very first part of the plot.