Thoreau relates time to a stream, "I drink at the stream; but while I drink I see the sandy bottom and detect how shallow it is."
The quotations marks (" ") make reference what Thoreau says.
The commas and the semi colons give the reader a better comprehension about what author is saying and feeling.
The other options put wrong puntuactions, which make the reader can confuse about what he is reading
Two Question
The unnecessary adjective is varied;
Many is a quantifier article
Are and offer are verbs
College and courses are nouns.
The only adjective is varied and also it is redundant in the sentence