[填空题]
(a) A brass plug is to be placed in a ringjhz0ki.(v ff/ made of iro+pg.kx9p20gld obgy 8 t3.4ppxb5 ci vn. At 20 $^{\circ} $ C, the diameter of the plug is 8.753 cm and that of the inside of the ring is 8.743 cm. They must both be brought to what common temperature in order to fit? $^{\circ} $ C
(b) What if the plug were iron and the ring brass? $^{\circ} $ C