A person vibrates the end of a string sending transverse waves down the string. If the person then doubles the rate at which he vibrates the string while maintaining the same tension , the speed of the waves
(a) doubles and the wavelength is unchanged
(b) doubles and the wavelength doubled
(c) doubles while the wavelength is halved
(d) is unchanged while the wavelength is doubled
(e) is unchanged while the wavelength is halved.