英语翻译：截止到九月底,他们已经去过美国十次了

By the end of September, they've already visited the U.S. ten times.

Vicky

They had been to USA ten times by the end of September.

by the end of september, they have been to USA 10 times

They had been to the USA for ten times by the end of September. (因

为九月已经过去了，发生在九月之前的事用过去完成时）

By the end of September,they had been to America ten times.
by表示到...时候这一意思时，应用于过去完成时。
如，到上周末，他们已经学了100多个英语单词了。
By the end of last week,they had learned over 100 English words.

By the end of September,they had been to America ten times.
by表示到...时候这一意思时，应用于过去完成时