Which one below explains when the QPR must be prepared:

a$)$ Quarterly reports must be prepared within $60$ days after the end of each quarter.

b$)$ Quarterly reports must be prepared at the end of each quarter.

c$)$ Quarterly reports may be prepared within $30$ days after the end of each quarter.

d$)$ Quarterly reports must be prepared within $3$ months after the end of each quarter.