In drawings, how do I make a perfectly horizontal or vertical line.  Some always end up as marginally off and I lose any attempt at a professional look.  Is there a hot key or option to just draw a horizontal line rather than an angled one?

Browser & Operating System (e.g. Firefox/Mac OSX): Google Chrome, Win 7 (64 bit)
Free consumer account (@gmail, @yahoo...) or Google Apps account (@yourdomain): @gmail
Describe the steps you took that produced this error:  Drawing any line in Docs-Drawings
Copy and paste any error messages: N/A