at the first time和for the first time的区别

at the first time和for the first time的区别
I fell in love with Zhangjiajie when i saw its scene ______.
A.for the first time B.the first C.by the first time D.at the first time
at the first time指的是很多次中的第一次
for the first time指的是生平中的第一次
那D