Answer:
When running an important cross country race, Jenny prefers to wear these sneakers instead of those sneakers."
Step-by-step explanation:
Considering the structure of the sentence and the blanks available in the sentence, it is easy to imply that the correct words for the blanks are "these, those". This makes the new and full sentence as "when running an important cross country race, Jenny prefers to wear these sneakers instead of those sneakers."
Considering the other options and placing them in the blanks doesn't make or produce a meaningful and correct sentence. So, the only correct option answer is to use option D.