Sunspots are the coolest parts of the sun. But in March, no sunspots were visible for 15 days. That is because a solar cycle is ending. In the solar cycle, there is a solar minimum and the solar maximum. The solar minimum is when there are very few sunspots. A solar maximum is when there are very many sunspots.

Points to remember:
*Prepositions
'IN' is used for unspecific times during a day, month, season, year while 'AT' is used to point out specific time

*Subject Verb Agreement
-Subjects and verbs must AGREE with one another in number (singular or plural). Thus, if a subject is singular, its verb must also be singular; if a subject is plural, its verb must also be plural.

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