SAT语法题Captive-bred whooping cranes have no parents to teach

the fact / a fact 跟同位语从句,它本身就是:事实为.
后面再跟 explain 总觉得很矛盾啊,您觉得呢,既然是事实,那还解释什么呢?
所以我建议改成
1)Captive-bred whooping cranes have no parents to teach them migratory habits,
a fact that they must be led on their first migration by human flying microlight aircraft.或
2)Captive-bred whooping cranes have no parents to teach them migratory habits,
explaining (=which explains)why they must be led on their first migration by human flying microlight aircraft.
3)当然没答案来得简洁易懂.
希望能帮到您

this fact explains why they must be led on their.... 这样可以。但是this fact explains结构很怪，最好能不用就不用。直接用，this explains why they must be led on their... 可以吗？或者干脆this explains why，不要"fact"
我看过最多的fact explai...