In a dual slop integrating type digital voltmeter, the first integrating is carried out for 10 periods of the supply frequency of 50 Hz. If the reference voltage used is 2 V, the total conversion time for an input of 1 V is _________
(a) 0.01 s
(b) 0.05 s
(c) 0.1 s
(d) 1 s