If I found a dinosaur skeleton one day, I would become a world-known archeologist.
Остальные варианты грамматически не верно построены, потому не подходят.
A.
1) had grown / cut;
2) had fed / started;
3) raised / saw / was falling;
4) had paid / didn’t forgive;
5) sold;
B.
1) had been;
2) was ringing / entered;
3) became / slways wanted;
4) fell / was preparing;
5) Did you pay / sent;
6) were you doing;
C.
1) was trying / had lost;
2) was talking / was cooking;
3) had been playing/ were;
4) found / used;
5) had stopped / was;
D.
1) was reading / heard;
2) found / brought;
3) had understood;
4) had bought / showed;
5) had been working / left;
6) had been wearing.
Посколько действие невозможное, то тут используется II Conditional:
( If + Past.Simple ) + ( would + V1 ( result part))