<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def to_cfunits(self, unit='hours', utcoffset=None):
 """Return a `units` string agreeing with the NetCDF-CF conventions. By default, |Date.to_cfunits| takes `hours` as time unit, and the the actual value of |Options.utcoffset| as time zone information: 'hours since 1992-10-08 15:15:42 +01:00' Other time units are allowed (no checks are performed, so select something useful):
 'minutes since 1992-10-08 15:15:42 +01:00' For changing the time zone, pass the corresponding offset in minutes: 'sec since 1992-10-08 13:15:42 -01:00' """

        if utcoffset is None:
            utcoffset = hydpy.pub.options.utcoffset
        string = self.to_string('iso2', utcoffset)
        string = ' '.join((string[:-6], string[-6:]))
        return f'{unit} since {string}'