Organ. An organ is a system of tissues that work together on a larger scale to do certain jobs within an animal's body. Examples of organs are the brain, heart and lungs. Anatomy is an example of a biology specialty concerned with this level.
Option D is correct.
A synapse is the opening between neurons that neurotransmitters pass through.
1 is b or 1/4 (I'd recommend checking a punnet square too)
That is correct, a good description of the HYPODERMIS. Hence many syringes get the name "hypodermic" needles.
