The above mentioned sentence would have Option C, “Doctor” as the answer.
In the sentence, there are three nouns which are given: the crowd, the doctor and the prince. While the crowd is a collective noun, the prince happens to be masculine in nature. The only noun which can be applied for both masculine and feminine, is the doctor. A lady doctor and a male doctor both are referred to as the doctor, in the same sense.
Hence, Option C is the correct answer.