✨ ベストアンサー ✨
1) If you (should) (need) my help, call me at once.
2) If the earth (were) (to) disappear tomorrow, I (would) not change my mind.
3) (Were) (I) rich, I would buy a house for my parents.
※Were(V) I(S) rich:倒置表現=If I were rich
参考にしてください。