Those who don’t get their sufficient sleep are actually sending a(n) to severe problems in their life.
A. invitation
B. warning
C. explanation
D. solution
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(答案→)A. invitation
B. warning
C. explanation
D. solution
解析：这题考查词义辨析：invitation邀请，诱因， warning警告，explanation解释， solution解决方法。句意是：得不到有效睡眠的人会诱发严重的问题。选A。