What is an indispensable necessity?

quite an interesting way to teach topic sentences, because the answer to this question is the best definition of a topic sentence that one can present, it is as if answering the questions taught you how to do it, this is some real teaching, it is terribly well-done.

the topic sentence in this paragraph is:

topic sentences writers stay on track and keep a paragraph from becoming an aimless collection of sentences about an idea.

which incidentally tells you what a topic sentence should be.

- "there are several movements that doris lessing was associated with. first of all, communism. she pursued her communist beliefs and included them in her writing, and was also a member of several communist book clubs. she is also strongly associated with feminism, her fight for equality and women's rights.

doris lessing is the kind of writer who has followers, not just readers. they have been engaged to her chiefly because of her involvement in major problems, such as politics and woman-ism."