Which of the following forces is responsible for keeping the planets in orbit around the sun?
a.
magnetism
b.
gravity
c.
friction
d.
electromagnetic force

This is not a descriptive investigation.

A descriptive investigation is a research strategy which can include a scientific question but it cannot include a hypothesis. In these observations are recorded without manipulating the variables and with no comparison of the data. This is mainly used to develop a idea by creating a three dimensional modal for natural phenomena like rock formation, electric circuit and animal behavior.

The given situation is not an example of the descriptive investigation because  here different sizes of the parachute explains a manipulated variable the effect of which can be measured on the dependent variable that is the time of the skydiver in the air. A manipulated variable should not be present in the descriptive investigation.