Included in the "dull" and the "difficult" categories were surveillance missions requiring time and a degree of persistence that crews of manned aircraft could not provide.
“枯燥”“困难”分类内的任务包括需要时间和相当程度的耐久性的监视任务，这是人工飞行器不能满足的。
A number of difficult situations can make the life of even the happiest person dull and miserable.
一些艰难的困境甚至会让那些最幸福的人感到生活无趣、糟糕。
I found English grammar dull and difficult.
我觉患上英文语法枯燥难明。
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