Read the following statement:
While start-ups have__________ reach, _____ they introduce ________ products, they open-up ________ markets.
Fill in the blanks meaningfully, in the above statement, from the following options.

We can see that the last two words are "new and "innovative" in some order. 
It would make more sense to say that they introduce innovative products and open up new markets, than the other way around. 

Narrowing us down to options B and D. 

Option B has "while they introduce", implying a contradiction down the line, which never comes in the sentence, eliminating the option. 

This leaves us with option D, which says that while start-ups have limited reach when they introduce innovative products, they open up new markets. Making a coherent sentence. 

Therefore, Option D is the correct answer.