Final answer:
Bicoid inhibits caudal expression during embryonic development by blocking of translation, which helps to establish the anterior-posterior axis in Drosophila embryos.
Step-by-step explanation:
The mechanism that bicoid employs to inhibit caudal expression during embryonic development is by blocking of translation, which is answer A). Bicoid protein functions as a transcription factor and an anterior morphogen in Drosophila embryos. It translates into a gradient and regulates the expression of various target genes, including caudal, by binding to its mRNA and preventing translation. This mechanism is critical as it contributes to the formation of the anterior-posterior axis in the embryo and delineates the head structures from the tail structures.