被烟草枯萎病菌侵染的烟株,在发病后期,病茎横切后可见木质部变成(),但皮层与薄壁细胞的幼嫩组织不腐烂(该病与低头黑病的主要区别)。
A.深黑色
B.浅黑色
C.深褐色
D.浅褐色
The government passes a law that allows a substantial subsidy for every cure of land used to grow tobacco. How does this program affect the long-run supply curve for tobacco?