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.
Developing Chinese: Elementary Comprehensive, Volume 2 (发展汉语初级综合). Second Edition. Published 2011. Written by Kai Yuhua and Lai Siping. Beijing Language and Culture University Press. 286 pages. Contains 20 lessons with around 400 words. ISBN: 9787561930779.