Port Lympne Reserve, which runs a breeding programme, haswelcomed the arrival of a rare black rhino calf . When the tiny creaturearrived on January 31, she becamethe 40th black rhino to be born at the reserve. And officials at Port Lympnewere delighted with the new arrival, especially as black rhinos are known forbeing difficult to breed in captivity .
上面一段摘自2021年英语高考考试全国卷II阅读理解B。请问这里为何用 to be born 而不需要 born 呢？这个“出生”不是已发生了吗？用不定式应该是指还没有出生或是将要出生吧？对于已发生的动作为何还可以用不定式呢？
这里用不定式主如果由于其前有序词 the 40th 修饰。譬如用序数the first修饰就是最典型的使用方法（大伙比较熟知）。如：
The school was the first one to be built in our town. 这是大家镇修建的第一所学校。
That is the first site to be excavated in here. 那是初次在这里挖掘的一处遗址。
The family of the deceased were the first to be told. 死者的家人是最早被告知的。
网友的句子意思：
When the tiny creature arrived on January 31, shebecame the 40th black rhino to be born at the reserve.
当这只小家伙于1月31日出生时，她成为了在保护区生的第40头黑犀牛。
不过，网友的句子不需要不定式的被动式，直接用过去分词也是可以的。譬如就在2021年英语高考考试全国卷II阅读理解B这同一篇文章就有如此一句，用的是过去分词 born（虽然前面有序数词 second 修饰）：
The adorable female calf is the second black rhino born this year atthe reserve. 这只可爱的雌性小牛是保护区今年生的第二只黑犀牛。
