--- I ______ so busily recently that I ______ no time to help you with your math. --- That’s OK. I can manage it by myself.
These continual _____ in temperature make it impossible to decide what to wear.
The illness from which Mary is suffering has now been _____ as hepatitis (肝炎).
A completely new situation is likely to _____ when the school leaving age is raised to 16.
. I must go now. _____, if you want that book I'll bring it next time.
Achieving a high degree of proficiency in English as a foreign language is not a mysterious _____ without scientific basis.