柑桔溃疡病病菌的侵入途径是（）。
A.皮孔
B.伤口
C.气孔
D.直接侵入
E.水孔
参考答案：A, B, C
微分方程y”-2y’-3y=0的通解为（）。
A.A
B.B
C.C
D.D
That was really a splendid evening. It's years ______I enjoyed myself so much.
A．when
B．that
C．before
D．since
