You can’t plain about being left out you don’t make any effort to share your joys and sorrows with others.
A. once
B. unless
C. when
D. though
网友回答
A. once
B. unless
(答案→)C. when
D. though
解析：句意，当你不能和别人分享你的快乐和痛苦时，你就不能抱怨被丢弃。Once一旦 unless除非 when 当……时 though尽管，根据题意，故选C。