Which of the following statements are correct ?

Correct statements are(a) A depressant prevents certain type of particle to come to the froth. e.g. NaCN is added as a depressant during separation of PbS and ZnS.(b) The solidified copper obtained from reverberatory furnace has blistered appearance due to evolution of SO2 during the extraction.     (b) and (d) are incorrect statements, and can be correctly stated as(c) Copper matte contains Cu2S and FeS .(d) Zinc can be extracted by reduction of ZnO with carbon.