Auxiliaries + perfect infinitives<br/><br/>Use the perfect infinitive of the verbs in brackets with a suitable auxiliary verb:<br/><br/>Example:<br/><br/>1. I've never seen a London policeman.~<br/><br/> You <b>(see)</b> one! You've been in London a week already!<br/><br/>1. I've never seen a London policeman.~<br/><br/> You <b>must have seen</b> one! You've been in London a week already!<br/><br/>Question:<br/><br/>2. We<b> (start)</b> yesterday (this was the plan); but the flight was cancelled because of the fog, so we're still here, as you see.<br/><br/>My answer:<br/><br/>2. We<b> could have started </b>yesterday (this was the plan); but the flight was cancelled because of the fog, so we're still here, as you see.<br/><br/>But the correct answer is<b> were to have started. </b>Could someone explain it to me?<br/><br/>Thanks in advance.