ジョンさんは 花（はな）を手（て）にして待（ま）っていた。
a. John was waiting and his hands looked like flowers.
b. John was waiting for an artificial hand made from plants.
c. John was waiting there like some flowers.
d. John was waiting there with flowers in his hand.
手（て）にする means “to hold” or “to get hold of.” In this example, it means the former, so the answer is d.
Other usage of 手にする include:
ペンを手にする = to take a pen in one’s hand
本を手にする = to hold a book in one’s hand
自由を手にする = to get grasp of freedom
