A. and

B. or

C. so

D. but

words

so

has

There are many kinds of forests in the world, but tropical rain forests are the most fascinating.

There are many kinds of forests in the world, for tropical rain forests are the most fascinating.

There are many kinds of forests in the world, or tropical rain forests are the most fascinating.

There are many kinds of forests in the world, so tropical rain forests are the most fascinating.

Animals need forests in order to live, or forests provide places to live and sources of nourishment.

Animals need forests in order to live, but forests provide places to live and sources of nourishment.

Animals need forests in order to live, for forests provide places to live and sources of nourishment.

Animals need forests in order to live, so forests provide places to live and sources of nourishment.

Acid rain, a product of air pollution mixing with rain to develop sulfuric acid, and is a threat, it has damaged some forests.

Acid rain, and a product of air pollution mixing with rain to develop sulfuric acid, is a threat, it has damaged some forests.

Acid rain, a product of air pollution, and rain to develop sulfuric acid, is a threat, it has damaged some forests.

Acid rain, a product of air pollution mixing with rain to develop sulfuric acid, is a threat, and it has damaged some forests.

People have been clearing forests for thousands of years, so deforestation has increased as the earth's population has increased.

People have been clearing forests for thousands of years, for deforestation has increased as the earth's population has increased.

People have been clearing forests for thousands of years, yet deforestation has increased as the earth's population has increased.

People have been clearing forests for thousands of years, or deforestation has increased as the earth's population has increased.

In order to help save forests, governments have set aside national parks, so groups replace felled trees with new ones.

In order to help save forests, governments have set aside national parks, for groups replace felled trees with new ones.

In order to help save forests, governments have set aside national parks, but groups replace felled trees with new ones.

In order to help save forests, governments have set aside national parks, and groups replace felled trees with new ones.

They are neither my schoolmates nor my friends.

They are either my schoolmates or my friends.

You can either go left or right.

You can neither go left nor right.

I went neither to the birthday party nor the wedding.

I went either to the birthday party or the wedding.

either .. or

neither .. nor