1.A
Seen from the top of the mountain,the city is very beautiful.
分析：作为条件/方式状语,主句（主干：主系表结构）主语为the city,是“物”,故状语部分用“省略式”被动语态
还原完整句式（条件状语从句）：When it is seen from the top of the mountain,the city is very beautiful.
2.C
Seeing from the top of the mountain,you will find the city very beautiful.
分析：接上,主句（主干：主谓宾+宾补）主语为you,是“人”,且参考其时态（will find）,系一般将来时态,故考虑状语部分用“省略式”现在进行时（或：一般现在时）,不可用一般过去时、现在完成时
还原完整句式（条件状语从句）：When you are seeing from the top of the mountain,you will find the city very beautiful.
如果说When you see from the top of the mountain,you will find the city very beautiful.
题外：考点1是主干与前置状语动词-主语一致；2是时态