This applet can help you answer questions from the worksheet, and visualize counterexamples. The link under the applet provides a hint on how to manipulate sides and angles. Worksheet link is also there.
Always refresh the applet before going to the next question.
Hint on how to manipulate objects:
http://people.cst.cmich.edu/marci1t/341/Hint_TrianCongr_Explorations.jpg
Worksheet: http://people.cst.cmich.edu/marci1t/341/TriangleCongruenceActivity.pdf