Ifinditamazingthatyoucan'tswim：that后接主语从句.可还原为Itisamazingthatyoucan'tswim或Thatyoucan'tswimisamazing.

　　HewasveryluckytosurviveYushuEarthquake：tosurviveYushuEarthquake为不定式作原因状语,表示Hewasverylucky的原因

　　怎么划分主谓宾？

　　Ifinditamazingthatyoucan'tswim：主句Ifinditamazing，主语I，谓语find，宾语it，宾补amazing.从句youcan'tswim，其中主语为you，谓语为can'tswim。HewasveryluckytosurviveYushuEarthquake:主语He，谓语was，状语very，表语lucky，补语surviveYushuEarthquake不好意思Ifinditamazingthatyoucan'tswim中是it作形式主语，不是主语从句