The correct answer is: If a doctor arrives in time, the patient can be saved.
The other options are incorrect because they do not express the same certainty as the correct option. The option “Had arrived” expresses a past event that did not happen, so it does not make sense in the context of the question. The option “Will arrive” expresses a future event that is not certain, so it is also not a good choice. The option “Do arrive” is grammatically incorrect, so it cannot be the correct answer.
The correct option, “If a doctor arrives in time, the patient can be saved,” expresses a conditional statement. This means that the outcome (the patient being saved) is dependent on the condition (the doctor arriving in time). This is the only option that expresses the certainty that is required in the context of the question.