Question

First I will send you the document ________________

. Then I will bill you.
: then I will bill you.
; then I will bill you.
then I will bill you.

Answer 1

Explanation:

all the options are same

Answer 2

First I will send you the document then i will bill you.

Option (d) is correct.

Explanation:

First I will send you the document ________________

(a)  .Then I will bill you.

(b) : then I will bill you.

(c) ; then I will bill you.

(d) then I will bill you.

First I will send you the document then i will bill you.

Then is used to refer the time. When you are talking about something related to time.