If b+ca+b=d+ac+d, then:<spanclass=′latex−bold′>(A)</span>a must equal c<spanclass=′latex−bold′>(B)</span>a+b+c+d must equal zero <spanclass=′latex−bold′>(C)</span>either a=c or a+b+c+d=0, or both<spanclass=′latex−bold′>(D)</span>a+b+c+d=0 if a=c<spanclass=′latex−bold′>(E)</span>a(b+c+d)=c(a+b+d)