Quickening usually occurs at:

Correct option is D

Quickening is the term used to describe the first movements of the fetus felt by the mother, usually occurring between 16-20 weeks of pregnancy. This is typically when the mother begins to feel the fetus moving, though it can vary slightly depending on the individual.
Explanation of options: (a) ✘ Incorrect. Quickening generally does not occur as early as 8-12 weeks. (b) ✘ Incorrect. Quickening usually happens later than 12-16 weeks. (c) ✘ Incorrect. 24-28 weeks is too late for the first fetal movements to be felt as quickening. (d) ✔ Correct. Quickening typically occurs between 16-20 weeks.