We had a casual conversation in the waiting room.

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　　①be casual about对......漫不经心

　　②casually adv. 偶然地；无意地；若无其事地

He tried to sound casual，but I knew he was worried.

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She is casual about winning the prize.

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2. obvious adj. 显然的，显而易见的

　　It_was_obvious_that he was suffering great pain when he talked.

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　　It was obvious that...属于"It＋be＋adj./n.＋从句"结构，该结构用法如下：

　　①it：为形式主语，真正的主语为后置的从句

　　②从句的引导词：that，when，where，why，how，whether，if等

　　【提示】　that引导从句时，仅起连接作用，不作成分，也无词义；whether/if引导从句时，有词义，起连接作用，但不作成分；其余的连接代词/连接副词有词义，起引导从句和充当句子成分的双重作用。

It is obvious that he is reluctant to leave his hometown.

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It is unknown whether he will join us in the discussion.

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It is still a mystery why he went abroad suddenly.

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　　It seems＋adj.＋that从句

　　It＋不及物动词(如seem，happen，turn out，occur等)＋that从句

　　It is＋名词性短语(如a pity，a fact，a wonder，an honor等)＋that...

　　It is＋adj.(如natural，obvious，possible，likely等)＋that从句

　　It is＋过去分词(如reported，believed，said，announced等)＋that从句

　　It is certain that she will do well in her exam.

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　　It is reported that he has won the game.

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