Adjective clause with preposition
Why, in some sentences, must we add a preposition before the "which" clause and why in some sentences must we not add a preposition before the "which" clause?A:
Betty Azar's Understanding and Using English Grammar, 3rd ed. (Pearson Education, 1999), explains very clearly how to use adjective clauses with prepositions. Click here to see the chart and explanation from page 269 of that grammar book.