6.
Grandmother's diary was a window to the past,
Example what the simile or metaphor means

metaphor

Explanation:

its saying something not true but it's almost exactly like it is

simile is an exasperation that is comparing with things with like or as.

Explanation:

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.