I guess becase in vacation time you are not able to access the net.
you could pay per month though, add cards, then study for one month (when you dont pay), then pay and add again...
Looks like the Great Firewall or something like it is preventing you from completely loading www.skritter.com because it is hosted on Google App Engine, which is periodically blocked. Try instead our mirror:
This might also be caused by an internet filter, such as SafeEyes. If you have such a filter installed, try adding appspot.com to the list of allowed domains.
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