植物病害病状大体上分为五大类型，即（）、（）、（）、（）和（）。
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微差爆破就是顺序起爆的炮孔或炮孔组之间在时间上相差仅（）的爆破；比起以秒为单位的秒差爆破来，其延期时间要短得多，但又不同于（）。
Which of these statements best describes the major difference between an IPv4-compatible tunnel and a 6to4 tunnel？（）
An IPv4-compatible tunnel is a static tunnel， but an 6to4 tunnel is a semiautomatic tunnel.
B. The deployment of a IPv4-compatible tunnel requires a special code on the edge routers， but a 6to4 tunnel does not require any special code.
C. An IPv4-compatible tunnel is typically used only between two IPv6 domains， but a 6to4 tunnel is used to connect to connect two or more IPv6 domains.
D. For an IPv4-compatible tunnel， the ISP assigns only IPv4 addresses for each domain， but for a 6to4 tunnel， the ISP assigns only IPv6 addresses for each domain.
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