In the following question, a sentence / a part of the sentence is given in bold. Below are given alternatives to the underlined part which may improve the sentence. Choose the correct alternative. In case no improvement is required, choose No Improvement option accordingly.
Not only the robbers robbed the tourist of his purse but they also wounded him grievously.

• Not only did the robbers robbed.

• Not only the robbers rob

• Not only did the robbers rob

• No Improvement