题目

设a=3x2﹣x+1，b=2x2+x，则（ ）                                                      A．a＞b                       B．a＜b                       C．a≥b                         D．a≤b   答案：C【考点】不等式比较大小．                                                                    【专题】计算题；不等式．                                                                      【分析】作差法化简a﹣b=x2﹣2x+1=（x﹣1小麦抗病（B）和无芒（R）分别对感病（b）和有芒（r）为显性，两对性状独立遗传。现将抗病无芒小麦和感病有芒小麦杂交得到的F1自交，F2的表现型及比例为抗病无芒∶抗病有芒∶感病无芒∶感病有芒＝9∶15∶15∶25，则亲本的基因型为A. BBRR×bbrr B. BBRr×bbrrC. BbRR×bbrr D. BbRr×bbrr