Hedgehog (Hh), and many other signaling pathways, were originally discovered in Drosophila. Hedgehog

Hello!

I have a couple of questions that I have NFC on:

Part A
Hedgehog (Hh), and many other signaling pathways, were originally discovered in Drosophila. Hedgehog was so named because of bristles all over the early embryo, resembling a hedgehog. It works, with other genes, to develop the anterior-posterior axis of the embryo.
The mutant develops bristles all over the embryo instead of just in a stripe toward the anterior. Thus Hh is a segment polarity gene. The hedgehog gene family in vertebrates is involved in development of central and peripheral nervous system, skeleton limbs, lungs, skin and germ cells. Shh (Sonic hedgehog) is responsible for major development of brain, spinal cord, and skeleton and is received at the membrane via the patched receptor (PTCH). In the absence of Shh, PTCH inhibits the activity of the pathway, while binding of Shh allows signal transduction to go forward.
In humans, holoprosencephaly is a developmental disorder involving incomplete cleavage of the forebrain, leading to the abnormalities of brain and facial structures. From the above, which abnormalities of genes must be involved?
    A) Shh only
    B) some other member of the Hh gene family
    C) Shh in combination with PTCH
    D) PTCH only
    E) either Shh or PTCH

**I thought Part A was A (Shh only) but it's not. I'm thinking its C, combo of Shh and PTCH but I'm not sure.**

Part B
In Drosophila, mutation screening usually involves use of a balancer chromosome that includes three elements: a set of overlapping inversions, an easily recognized dominant mutation, and a recessive lethal mutation that prevents balancer homozygotes from surviving. Which one, or combination, of these elements is necessary and sufficient to suppress crossovers?
In Drosophila, mutation screening usually involves use of a balancer chromosome that includes three elements: a set of overlapping inversions, an easily recognized dominant mutation, and a recessive lethal mutation that prevents balancer homozygotes from surviving. Which one, or combination, of these elements is necessary and sufficient to suppress crossovers?
   A) inversions plus dominant
   B) lethal plus inversions
   C) dominants
   D) inversions
   E) lethal recessive

Part C
Suppose a gene from a cow is introduced into a frog. This results in a ________ transgene.

From: MasteringGenetics chpt 17 questions! (reverse genetics & transgenic organisms)