种庄稼要用水,但这一地区今年老不下雨,怎么办?一种办法是灌溉,以补天不下雨的不足。另一种办法是改种耐旱作物,此时所种作物与环境相适应。这两种措施分别是
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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