Final answer:
If Marlene is treated immediately with penicillin, the baby will be protected from syphilis.
Step-by-step explanation:
If Marlene is treated immediately with penicillin after contracting syphilis during her 3rd month of pregnancy, the baby will be protected from syphilis. Penicillin is the recommended antibiotic for treating syphilis, and it has a high success rate at preventing mother-to-fetus transmission. In this case, the prompt administration of penicillin will help ensure that the baby does not contract syphilis from Marlene.