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').

[EX Q]: Cyclic neutropenia tends to occur every three weeks and last ____ to six days at a time.\Question: Choose the right answer from options given a) six b) four c) five d) three
[EX A]: d

[EX Q]: Heme is made of ____ pyrrole groups united to form a porphyrin ring.\Question: Choose the right answer from options given a) five b) four c) eight d) six
[EX A]: b

[EX Q]: Water dissolves about ____ part in seven thousand parts, and receives a brown color.\Question: Choose the right answer from options given a) eight b) one c) seven d) nine
[EX A]:
b