When a hot liquid sample is mixed with a cold one , the temperature of the mixture

Question

$(a)\;first\;decreases\;then\;becomes\;constant\qquad(b)\;first\;increase\;then\;becomes\;constant\qquad(c)\;continuously\;increases\qquad(d)\;is\;undefined\;for\;sometime\;and\;then\;becomes\;nearly\;constant$