a,b,c全正，a/丨a丨﹢丨b丨/b﹢c/丨c丨=3a,b,c两正一负，a/丨a丨﹢丨b丨/b﹢c/丨c丨=1a,b,c全一正两负，a/丨a丨﹢丨b丨/b﹢c/丨c丨=-1a,b,c全负，a/丨a丨﹢丨b丨/b﹢c/丨c丨=-3a/丨a丨﹢丨b丨/b﹢c/丨c丨可能的值有4个，选D
