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: Ascidian tunicates come in ____ main forms.\Question: Choose the right answer from options given a) three b) zero c) four d) eight
Example Output: a

Example Input: Mosquitoes have ____ distinctive life stages, with the first three stages being spent in the water.\Question: Choose the right answer from options given a) four b) zero c) nine d) five
Example Output: a

Example Input: Natural hafnium contains ____ isotopes.\Question: Choose the right answer from options given a) one b) six c) four d) nine
Example Output:
b