Present and past speculation

The key ________ be somewhere here, but I can't find it right now .

You _____remember me - we met on a trip to China last year.

I ______ my mobile phone at the hotel, but I don't remember.

Susan has been travelling for the last two weeks - she must ____ very tired by now.

You can't ______ Joe in town at noon - he was at home with me.

You failed the exam,so your answers ____ have made been wrong.