89일차. ♣ Unit 6. Hotels - LESSON 3. GETTING HELP FROM THE CONCIERGE - [Extra information with 'which'] ※ Adding information with *which* *To add extra information to a sentence, you can use a clause with which. Notice that, because these clauses add non-essential information, there is a comma (,) to mark off the clause. The river cruise, which would show you some of London's most famous monuments..