We have a high regard for Mr. Black because he always tries to ________ his principles.
So far all cloned animals have suffered from some different serious disorders, _______ dying soon after birth.
When asked to explain ________ he does to make his students so fascinated with his lessons, the teacher paused and thought deeply.
_______ to her own work, she spent little time with her children.
--- Are you happy with this laboratory? --- Not a little. We can’t have _______.
Medicine shouldn’t be kept _______ it is accessible to children.