用it作形式主语的用法改写下列各个句子
①To learn something about the use of “it” is necessary.
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②Crying over spilt milk is no use.
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③That the boss was behaving pretty strangely struck me.
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④Whether you come or not doesn’t interest  me.
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⑤Tom is believed to win the race.
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⑥That a picture is worth a thousand words is not always true.
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