Measurements of a plant's growth over a two-week period represent
a. qualitative data.
b. variables.
c. hypotheses.
d. quantitative data

The correct answer would be d. quantitative data.

Quantitative variables refer to the measures of values which can be expressed as numbers.

These include numeric variables such as how much, how many, how often et cetera.

For example, the growth of a plant, that is, a measure of its height over two weeks period.

but there is no

i guess you forgot putting it.