We have the following statements:

I $$ In a calendar convention the number of days in a year is always $365.$

II $$ In a banking convention the number of days in a month may not be equal to $30.$

III $$ Always the number of days in the calendar convention is greater than in the banking convention.

IV $$ For creditors calculating the fraction of a year it is always better to use $($in denominator$)$ the number of days in a year according to banking convention.

a$)$ all are false

b$)$ only IV is true

c$)$ all except IV are true

d$)$ only III is true