Question 1:
The correct answer is C.
In this passage, the word "youthful" implies that Grandma's curiosity has vitality or freshness of the youth.
Question 2:
The correct answer is A.
"Timely" is used in this excerpt to show that the repair was done right on time, since, had it not be done at that moment, the snowplow would not have been available to clean to snow brought by the blizzard that burried the town the next day.
Question 3:
The correct answer is C.
This is the best way to revise the sentence because it uses the relative pronoun "that" to add information about the subject directly before it: the cake.