Student or Learner
1:I didn't know which how I should react in that situatin.
2: I didn't know how I should've reacted in that sitiuation.
1:Senegal is in the west cost of africa.
2:Senegal is on the west cost of africa.
1:I didn't know if you liked novels.
2:I didn't know if you like novel.
Note that it is coast, not cost.