The correct answer is C.
Neap tides are those tidal waves that have the smallest range between high tide and low tide and occur twice in a month.
Spring tides are the tidal waves that have the biggest range between high tide and low tide, and are also seen to occur twice a month.
If the moon revolved twice a month around the Earth, it would mean that the lunar cycle would be of 15 days -meaning 30 days/a month would incorporate two lunar cycles. As the spring and neap tides occur twice each in one lunar cycle, they will occur four times in 30 days.
