Use the Following to Answer Questions

Multiple Choice

Use the following to answer questions :
Refer to the figure below showing a stage in limb development in a human embryo.
-The substance secreted by the ZPA is _______ and the concentration of this is lowest at the region labeled _______.

A) the protein Sonic hedgehog;2
B) the Shh gene;2
C) the transcription factor that turns on the Shh gene;1
D) the ZPA1 protein;2
E) the protein product of the zone of polarizing activity;1