Click textbox to show answer and highlight related text
Here are my thoughts:


Most importantly from the first look at the code: Use proper variable names. No one knows what you mean with EEE, xxx or e2. And while you are at it: in JavaScript it's a convention to start variable names with a lower case letter.
Don't make up attributes such as "answer" - you can't say if an unknown browser can work with them. At least you should adhere to HTML5 and prefix the custom attribute with data-. 
name is not a valid attribute for span (or any other object other than form elements). Unfortunately there is no simple, cross-browser alternative for selecting multiple elements. The easiest soltuion with be to use a class and getElementsByClassName, however the latter isn't supported by all browsers yet, but there are implementations for the non-supporters easily available on the web.
The "Click" text is bad for two reasons: A) You can't actually click on it and B) texts such as "click here" is bad UI. Instead wrap the text together with the checkbox in a &lt;label&gt; element, such allows the user to click on the text to activate the checkbox and use a text such as "Show solution" instead.
Finally, there are more elegant ways to switch on the answers. Instead of looking of a specifc ID, set (or remove) a class on an element surrounding the question and use CSS to highlight/show the sub elements. Example: http://jsbin.com/ayoqem/7/edit