After years of research, he found the key ____ differences between species.
| A．to explain | B．to explaining | C．of explaining | D．explaining |
_____ the English examination I would have gone to the concert last Sunday.
| A．In spite of | B．But for | C．Because of | D．As for |
Your help is _____ for the success of the project.
| A．indispensable | B．indicative |
| C．inevitable | D．inherent |
When she heard from the hospital that her father had died, she _____ into tears.
| A．burst | B．went | C．exploded | D．fell |
He _____ his engagement just before the wedding.
| A．broke out | B．broke away from |
| C．broke off | D．broke up |
The reference she made to her friend, the poet, was interesting but too _____ for anyone to appreciate.
| A．drastic | B．dull | C．obscure | D．distinct |