Which sentence is not correctly punctuated?

a.
i forgot my lunch, but dad brought it to me.

b.
i worked hard all morning, and i still had not finished by lunch.

c.
it rained yesterday, but we marched in the parade anyway.

d.
the spider is not an insect it is an arachnid.

To choose a good persuasive essay topic, begin with a big idea, narrow it down, and a. then narrow it down more; it is impossible to have a topic that is too narrow. b. do some research to see what you should write about c. specify-ask a question you want answered in your argument