--- He worked out such different questions at a very young age.--- Oh, he ______ a very smart student then.

--Honey, stay home before I return. ---I _______, mum. 

----Whose is that book? ----It _________ belong to Lucy. Her name is on it.

— Who _____ be phoning us at this time of night? — It might be your sister. 

One of the National Health Regulations is that public schools ______ actively create conditions for sports facilities opened to the public.