Can I use one domain with different extensions for google adwords and not have my QS dropped

example:

mydomain.com/keyword1
mydomain.com/keyword2
mydomain.com/keyword2
etc...

or

keyword3.mydomain.com
keyword4.mydomain.com
keyword5.mydomain.com

Sure, you can use subdomain and it won't affect your QS.
At least that's how I found from my test

I'd preffer this btw

keyword3.mydomain.com
keyword4.mydomain.com
keyword5.mydomain.com

Dont worry Go ahead and use subdomains.For Google adwords ,landing page content matter. Domain or subdomain is very not focus. But Good domains/sub help in getting better ctr. and Better CTR means Low cost per click.

i tried to cover every thing.