什么是内折.外折和对折?
纸盒折叠成型后,纸板底层为盒内角的两个边,而面层为盒外角两个边,则为内折反之则为外折.如果纸板180度折叠后,纸板两底层相对,则为内对折反之为外对折。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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