Given a sentence with a missing word, pick the answer option that best fills out the missing word in the sentence. Indicate each answer with its index ('a', 'b', 'c', 'd').

Example Input: Most herbal formulas contain ____ to twelve herbs in various combinations.\Question: Choose the right answer from options given a) four b) no c) seven d) six
Example Output: d

Example Input: Mothers usually give birth to one, two, or ____ babies at a time.\Question: Choose the right answer from options given a) three b) zero c) five d) ten
Example Output: a

Example Input: Medical science takes ____ months or more to create a vaccine once a new strain appears.\Question: Choose the right answer from options given a) one b) no c) eight d) ten
Example Output:
c