Answer: Dr. Naismith would have been surprised, if he had known how popular basketball would become.
Explanation:
The best way to combine these two sentences is to put a comma between them.
When joined together, these two sentences form a third conditional sentence.
In a third conditional sentence, one part of the sentence contains 'would have' + past participle <em>(would have been surprised)</em>, while the other part of the sentence contains 'if' and past perfect form of the verb (<em>if he had known</em>). Third conditional sentences are used to talk about impossible outcomes. Dr. Naismith was a physical educator who died in 1939. Therefore, the scenario of him witnessing the popularity of basketball is not possible.
