Final answer:
During weeks 28-31, the fetus undergoes significant development, including the completion of bone development and a substantial increase in body fat. The fetus measures approximately 28 cm (11 in) from crown to rump during this period.
Step-by-step explanation:
During weeks 28-31, the fetus is developing rapidly. By this stage, the bones of the fetus have completed their development and the body fat has increased substantially. The fetus measures around 28 cm (11 in) from crown to rump and exhibits approximate body proportions of a full-term newborn, although still leaner. This is a crucial period for the growth and development of various organs and systems in the fetus.