Sentence! HELP!?

1.You will need to apply online. To do ___ , please click on the following link.

it
one
this
such
2.___ director of Customer Services, I would like to thank you for your recent email.

How
Like
As
Being
3. ___ the meeting started late, we will continue for fifteen minutes or so.

For
Why
As
The reason
4. I will ___ that you are credited with this amount.

sure
ensure
insure
make
5. The office may be closed. If _____, leave the key in the letterbox.

so
is
it's
this