He wants to know what situation calls for use of the perfect tense.

他想知道在什么情况下需要用完成时态。

youdao

The present and past perfect tenses both belong to the perfect tense.

现在完成时和过去完成时都属于完成时态。

youdao

'I have eaten' is the present perfect tense of the verb 'to eat', 'I had eaten' is the past perfect and 'I will have eaten' is the future perfect.

I have eaten是动词eat的现在完成时；I had eaten是过去完成时；I will have eaten是将来完成时。

《牛津词典》

But to many, many others the explorer's courage, optimism and enthusiasm were the perfect distraction from a world still bruised by World War II and nervously watching the increasingly tense standoff between the United States and Soviet Union.

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Adding to the stress is the complexity of the grammar, especially the far-from-perfect spelling system hellish past tense riddled with irregularities.

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Having defied the distraction of a match-fixing scandal at home and beaten hosts Germany in a tense semifinal, the Italians held their nerve once again to convert five perfect penalties and win the World Cup for the fourth time.

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