"otherwise" vs "or else"

[Nessie]

Plesae have a look at this multiple choice question:

Please be quiet, ... I won't tell you the story
a. unless
b. otherwise
c. if not
d. or else
=> I chose d for this, but when I looked up the word "otherwise" in my OALD, here is an example for the word that I found:
Shut the window, otherwise it'll get too cold in here

=> I used to think that "otherwise" can just be used after a full stop. But if so, this multiple choice question must have two correct answers...
_________________
... something we never have again, I know... I guess I really really know..

Sorry seems to be the hardest word...

[Yankee]

Hi Nessie

There seem to be varying opinions about 'otherwise'.
The site below, for example, seems to recommend using a semi-colon in a sentence such as yours:
http://web2.uvcs.uvic.ca/elc/StudyZone/410/grammar/colons.htm

The Random House and Cambridge dictionaries both state that 'otherwise' can be used as a conjunction, and both give examples using a comma.
.

[Nessie]

So the question has two correct answers?

Haha, I know what you're going to say, Amy => another badly designed exercise from Nessie
_________________
... something we never have again, I know... I guess I really really know..

Sorry seems to be the hardest word...

[Yankee]