What is the key event that establishes the dorsal side of the embryo in Drosophila?
1) A Gurken binds to Torpedo which delivers a signal that represses the expression of Pipe.
2) B Gurken binds to the Pipe protein and directly represses its function.
3) C Torpedo prevents Gurken from entering the cell which represses Pipe.
4) D Gurken binds to Torpedo which increases Pipe expression.