During the second trimester, which fetal development occurs?

• A. Retina develops distinct layers
• B. Lungs start to produce surfactant
• C. Eyelids open and close
• D. Gender determination is typically made

Answer: (A)

The main idea here is understanding what fetal development milestones typically occur during the second trimester. The retina developing distinct layers is a clear sign of neural maturation in mid-pregnancy. As the nervous system grows, the retina differentiates into its layered structure (with the various neuronal layers forming in an organized way), which is a hallmark of the fetus's ongoing brain and eye development during this period. This layering reflects maturation that is clearly progressing in the second trimester, making it the best fit among the options.

Lungs producing surfactant tends to become functionally significant a bit later in the second trimester and into the third, as the fetus readies for breathing after birth. Eyelids opening and closing happens toward the end of the second trimester, and gender determination is typically identified by ultrasound around mid-pregnancy but isn’t a developmental change in the same way as neural differentiation. These nuances make the retinal layering the most representative second-trimester milestone.