“三系“杂交水稻不育系繁殖，就是以不育系用母本，保持系作父本进行杂交生产不育系种子的过程。
参考答案：对
—It’s a fine day today. Shall we go swimming?
—______ But we need to be home before six o’clock.
A．Have a nice time!
B．Not at all.
C．You are right.
D．Good idea!
请写出下列主要金属矿物的化学分子式：紫硫镍铁矿、黄铜矿、黄铁矿、镍黄铁矿、磁黄铁矿。
