We must take two aspects into consideration, both of __________ associated with the safety of the students .
| A．which | B．whom | C．that | D．them |
I didn’t manage to do it______you explained how.
| A．until | B．unless | C．when | D．before |
.Don’t stop______you meet with a word you don’t understand.
| A．at that time | B．each time |
| C．sometimes | D．when every time |
Don’t be afraid of asking for help ______it is needed.
| A．unless | B．since | C．although | D．when |
He made a mistake, but then he corrected the situation ______it got worse.
| A．until | B．when | C．before | D．as |
The thought ______he might be a scientist some day encouraged him to study hard.
| A．whether | B．that | C．how | D．why |