关系R如下：ABCDa1b1c1d1a1b2c3d4a2b1c1d3a3b1c2d2a3b1C3d4a1的象集是：A、{（b1）, (c1), (d1) }B、{(b1, c1), (b2, c3) }C、{（b1, c1, d1）, (b2, c3, d4) }D、{（a1, b1, c1, d1）, (a1, b2, c3, d4) }