It was________of Michael to inform us of his delay in case we got worried.
It is pretty well understood_______controls the flow of carbon dioxide in and out of the atmosphere today.
Mary got into acting purely _____________.
It is no use thinking about your ________ youth.
---Must he come to sign this paper himself? ---Yes.He______ .
I wonder how he could __________ not handing in his maths exercises yesterday, for his maths teacher is always strict with his students.