Final answer:
Placenta previa involves the placenta covering the cervix and can present as painless bleeding, while placental abruption involves the detachment of the placenta from the uterine wall and is associated with severe abdominal pain.
Step-by-step explanation:
Placenta previa and placental abruption are two different obstetrical conditions that can occur during pregnancy. Placenta previa occurs when the placenta partially or completely covers the cervix, the opening to the uterus, leading to potential complications such as antepartum hemorrhage. This condition typically presents as painless bleeding after week 24 of pregnancy. On the other hand, placental abruption is a condition where the placenta detaches from the uterine wall before delivery, which can cause severe abdominal pain and is dangerous for both the mother and fetus. Answering the student's question, option (b) Previa is painless bleeding, while abruption is associated with severe abdominal pain captures the key differences between the two conditions.