--- Could you tell me why I am constantly yawning this afternoon? ---Yawning ______ an indication that your body lacks oxygen and needs a rest.
The good thing about today’s children is that they can_____ very easily to new environments.
As a teacher, it is my _________ to make the students devoted to their study.
The research lacksevidence,and therefore,its conclusions are doubtful.
A good friend should be kind and helpful. _________ is my mother.
Though he is ill,he has not quit.