Fetal nutrition via placenta and cord; protection via cord support and amniotic cushioning

Steps:

• Nutrients reach the fetus through the placenta, which exchanges with maternal blood, and the umbilical cord, which transports them.
• The umbilical cord supports the fetus by anchoring it, while the amniotic sac cushions against mechanical shocks with fluid.
• Label Q as umbilical cord (feeds and supports), R as placenta (feeds), S as amniotic sac (protects).
• Thus, feeding uses Q and R; protection uses Q and S.

Why B is correct:

• Option B matches the dual roles: umbilical cord (Q) aids nutrient delivery with placenta (R) and provides positional support, while amniotic sac (S) absorbs shocks per embryonic development biology.

Why the others are wrong:

• A: P (likely uterus) and Q do not feed; R (placenta) and S (sac) mix feeding with protection incorrectly.
• C: R and S focus on placenta/sac, ignoring cord's feeding role; P and Q misassign protection.
• D: S and P reverse feeding/protection; R and Q wrongly pair sac/uterus with cord for shocks.

Final answer: B