Answer: B. Two weeks
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Step-by-step explanation:
It takes approximately 29.5 days for the moon to do a full orbit around the earth. This is about 4 weeks because (29.5)/7 = 4.214; to put it another way, it takes about a month for the moon do a full cycle.
So when going from a new moon to the next new moon, that's four weeks. We cut this in half when going from a new moon to a full moon (because such a duration is half the full cycle). Therefore, the answer we want is 4/2 = 2 weeks.
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Another approach is to search out "moon phase charts". You can also search out "lunar calendar" to have it show when the next full moon and new moon will occur. At this present time (October 2021), the next full moon is October 20th and after that the next new moon is November 4th. This is a timespan of 15 days or 15/7 = 2.14 weeks, which rounds to 2 weeks.