——When did you buy this computer? It looks so new.——I it for only a couple of days. My sister bought it for me as a birthday present.
A:bought
B:have bought
C:have had
D:had
根据植物茎的性质,可将植物分为____与____等。
读法国地图,分析完成下列问题。
一件产品要经过2道独立的加工工序,第一道工序的次品率为a,第二道工序的次品率为b,则产品的正品率为( )