He tried his best to solve the problem, _______difficult it was.
A. however B. no matter
C. whatever D although
The government requested that all the people ___________ in any indoor public area.
| A．not to smoking | B．not smoke | C．not smoking | D．to not smoke |
Scientists study ___________ human brains work to make computer.
| A．when | B．how | C．that | D．whether |
A girl on the bus begin to sing a pop song and soon all the other students _________.
| A．majored in | B．joined in | C．came in | D．handed in |
---Why were you late for school today?
----It was ________ I help catch a thief on the bus.
| A．since | B．as | C．for | D．because |
To tell the truth, it’s the first time that I _______ western food.
| A．had | B．had had | C．have | D．have had |