1）D。B的Rf值=9/18=0.5,A:B=1.5,A的Rf值=0.5*1.5=0.75，A的展距=18*0.75=13.52）A。A的Rf值=7.6/16.2=0.47,A的斑点应该在14.3*0.47=6.72
