There are three legs to the temperature change of water from -10&#186;C to 20&#186;C labelled "A" as the first leg, the warming of ice to 0&#186;C, "B" as the melting of ice to water at 0&#186;C, and "C" as the warming of water from 0&#186;C to 20&#186;C.
(C; labelled; A" as the first leg)
C
labelled
A" as the first leg