Choose the correct word to complete the passage

I began my teaching career nearly ten years old. I spent six years teaching in a remote village (1) ______the villagers were very poor and the living standard was low. Sometimes, I was very disappointed (2) ______bad living condition and low pay. I am really homesick. However, at that time, with my youth enthusiasm, I tried my best to devote myself to the noblest career, that (3) ______ “teaching”. I love my poor little students. They were living in poverty but they could not (4) ______from empty mind.

Sometimes, I was very disappointed (2) ______bad living condition and low pay.

However, at that time, with my youth enthusiasm, I tried my best to devote myself to the noblest career, that (3) ______ “teaching”.

They were living in poverty but they could not (4) ______from empty mind.

Read the passage and choose the correct answer for each question

The Stone Age was a period of history which began in approximately two million B.C and lasted until 3,000 B.C. Its named was derived from the stone tools and weapons that modern scientists found. This period was divided into the Paleolithic, Mesolithic and Neolithic Ages. During first period (2,000,000 to 8,000 B.C), the first hatchet and use of fire for heating and cooking were developed. As a result of the Ice Age, which evolved about one million years into the Paleolithic Age, people were forced to seek shelter in caves, wear clothing and developed new tools.

During the Mesolithic Age (8,000 to 6,000 B.C), people made crude pottery and the first fish hooks, took dogs hunting, and developed the bow and arrow, which were used until the fourteenth century A.D.

The Neolithic Age (6,000 to 3,000 B.C) saw humankind domesticating sheep, goats, pigs and cattle, being less nomadic than in previous eras, establishing permanent settlements and creating governments.

With what subject is the passage mainly concerned?