.________ gas leaks and similar accidents should occur, some responsible persons should regularly inspect all the laboratories.
| A．Unless | B．In case | C．Provided | D．Until |
______the address, Tom sent the email to his teacher.
| A．Having checked | B．Checked | C．Being checked | D．To check |
They all wanted to stop working because they were tired, but______of them would say sl.
| A．any | B．some | C．none | D．neither |
．______Hard you may try, you can’t possibly persuade Tom to give up smoking, for he is so addicted to it.
| A．Whatever | B．However | C．Whichever | D．Whenever |
Every year, Tom remembers to have some flowers______to her mother on her birthday.
| A．send | B．sent | C．sending | D．being sent |
It’s not easy to learn English well. ______as much as possible is necessary.
| A．Having read | B．Read | C．Reading | D．To have read |