Choose the correct alternatives :
(a) Alloys of metals usually have (greater/less) resistivity than that of their constituent metals.
(b) Alloys usually have much (lower/higher) temperature coefficients of resistance than pure metals.
(c ) The resistivity of the alloy manganin in (nearly independent of/ increase rapidly ) with increase of temperature.
(d) The resistivity of a typical insulator (e.g. amber) is greater than that of a metal by a factor of the order of `(10^(22) or 10^(3))`.