我的妹妹很可爱用英文表达是：My sister is very lovely；
sister：n. 姐; 妹; (称志同道合者)姐妹; 护士长。
lovely：adj. 美丽的; 优美的; 有吸引力的; 迷人的; 令人愉快的; 极好的; 亲切友好的; 慷慨大方的; 可爱的。
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She doesn't play as well as her sister.
她演奏得不如她姐姐。
My sister and I used to quarrel all the time.
我和妹妹过去老是吵架。
My sister came along just to give me some moral support.
我姐姐只是过来给我一些道义上的支持。
How lovely to see you!
见到你多么让人高兴！
You've got yourself into a lovely mess, haven't you?
你惹的这麻烦可真够瞧的，是吧？
It was no hardship to walk home on such a lovely evening.
在这么一个宜人的傍晚步行回家一点也不辛苦。
