Before the operation of the Suez Canal, the sea route from Europe to India was much longer as ships had to bypass the southern tip of Africa, passing through the Cape of Good Hope (Cape Town).
- Starting from London (III), ships would travel around the Cape of Good Hope (I) at Cape Town.
- From Cape Town, the next stop would be Mombasa (II), and then the ships would arrive at Mumbai (IV), which was a major port in India at the time.
Therefore, the correct order of ports before the Suez Canal operation is: London (III), Cape Town (I), Mombasa (II), and Mumbai (IV).
Thus, the correct option is (D).