What is the subject in this simple sentence?

vertebrates are animals with a backbone or spine.

a.
animals

b.
spine

c.
backbone

d.
vertebrates

the answer is industry

agamemnon was the leader of the greek troops in the trojan wars and orestes was his son. when agamemnon returned from the war, he was murdered by his wife's lover in conjunction with his wife. orestes could not stop them but he seeked vengeance for his father. after a long time, he found them and avenged his father while killing them. he killed his mother, but greek mythology claims that his act was just and he was spared the remorse and the guilt. there are a lot of similarities with the ulysses/telemachus father son pair. ulysses was also one of the leaders of the excursion to troy. he still has not returned home, but in a sense the suitors of penelope are marring his estate and his reputation. while penelope is faithful to ulysses, the suitors by taking hold of the palace and committing their shameful acts are dishonoring ulysses. in the same context, telemachus is asked just like orestes to restitution his father's honor, regardless of whether he is alive or dead. athena is him and encouraging him with this example and he himself feels the need to save his father

even though there may be variations in human emotions over time, the poem “ a contribution to statistics” by wislawa symborska suggests that the only unchangeable characteristic is mortality.

the author poses a distinction between the approximate and non-approximate numbers which correspond to our need for certainty in life and the difficulty of achieving it. our efforts to measure the exact often fail because the world is not always clearly structured .the poem seems to imply   that the only thing that is certain and has an exact number is death.