It was my sister who first had the idea to cycle along the Mekong River from where it begins to

It was my sister who first had the idea to cycle along the Mekong River from where it begins to

Who was the first to have to cycle along the Mekong River from where it begins to where it ends?
特殊疑问，应该 问的是谁是第一个。。。。所以要像上面那样提问

这是一个强调句型，对my sister 进行强调。所以在写成特殊疑问句时还应保持强调句型。追答Who was it that first had the idea to cycle along the Mekong River from where it begins to where it ends?此句中的that是强调句型中的，对人强调本可以用who，但为了避免重复句首的who，改为that。