Examples showing agreement without an object pronoun.

Question

In the Weekend Challenge: 'My plan for the day of the exam' one of the translations required is 'that I'll have chosen the day before'. 
The answes given are: 
'que j'aurai choisiS la veille'  OR 'que j'aurai sélectionnéS la veille'
There is no object pronoun in either of these answers, so why are the past participles 'choisi' and 'sélectionné' writen with an S added for agreement?
Thank you

Answer

Hi Stewart, it all hinges on the little pronoun "que". It is the stand in for the direct object in the relative clause. If it refers to a masculine noun in plural, you would need to have agreement between it and the participles.
I am not sure of the entire sentence, but when you check, you'll find that "que" refers to a masuline noun in plural.
-- Chris.

Answer

Thanks Chris, I now see that the use of 'que' was in the lesson after all!