A.they do not book their seats in advance
B.they do not sit on the seats they are supposed to take
C.they do not travel on the flight they have booked
D.they do not pay in advance for the seats they book.
第3题
高粱炭疽病的病菌一菌丝体在病残体内或其他寄主上越冬,也可以菌丝和分生孢子在种子上越冬。()
第4题
越冬或越夏的病原物,对经休眠进入生长季节的植物,引起最初次侵染,称为()。
A.病程
B.侵染程序
C.初次侵染
D.再次侵染
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