Chop block

[jTheUmp]

C is the correct answer.

Here's what might've happened:
1) you accidentally selected an incorrect answer.
2) you originally selected C, but then somehow accidentally selected a different answer without noticing it (the MN version of the test has this problem if you press an arrow key or scroll using the mouse wheel... I found out the hard way a couple of years ago)
3) The test answer key was incorrect and/or the person who created the answer key was using a rule book that's out of date (the simultaneous high-low block was legal in the free-blocking zone until about 2-3 years ago).