Answer:
In about 30 days
Explanation:
Assume Xavier sights a full moon today, it'll take around 29.5 days to see the moon at that size again.
Analysing each of the given options, only option D answers the question because 29.5 days can be rightly said to be about 30 days.
Or better still, 29.5 days approximates to 30 days.
