When people cut down big trees，new trees should be planted．      ，they will have no trees to cut down in the future．

A．If not            B．If so         C． If not so                    D．If don’t

 (2011年潍坊质量监测)When people cut down big trees，new trees should be planted.________they will have no trees to cut down in the future.

A．If not                           B．If so

C．If no so                        D．If don’t