Vivipary means germination even when attached to the mother plant. Usually the saline marsh plants (Halophytes) have their seeds growing even when they are inside the fruits attached to the tree.

The hormone adrenaline also called epinephrine is known as a stress hormone. In emotional upsets( like fear, anger etc.) this hormone is poured into the blood and it accelerates heart beat. The hormone acetylcholine decelerates heartbeat rate.

Here from the above options, Algae is an Autotroph.

Autotrophs : 

An Autotroph is also called as Producer, is an organism that produces complex organic compounds from simple substances present in its surroundings, generally using energy from light or inorganic chemical reactions.

Tooth Enamel is the hardest and most highly mineralized substance in the human body. It is a tissue and not a bone. This tissue has high mineral content which makes it hardest substance.

Femur and Temporal bone of the skull are the hardest bones of the human body.