Is it rude to forward an email to someone left out of the email? I've emailed a professor/TA and cced my peers or also a different professor/TA and cced another professor/TA. However, sometimes I get emailed back only to my email, not the person cced, would it be rude to forward the email to the person cced?
I'm not sure in some cases I'm not sure why they would respond only to me when the question for example was relevant to all my group members, or as well, when I email a professor (A) a question on a project I'm working on with another professor (B) but professor A only replies to me instead of professor B cced.
I want to forward the email but I'm not sure what the person cced would think of my trustworthiness, especially considering she's my professor/supervisor.
This is a bit subtle, since email client software is different for different people. A lot of people replying to an email don't take the time and effort to look at who (all) will get the mail.
In the general case, for a group that communicates frequently, you can, perhaps, establish guidelines. In the specific case, you could ask the professor that sent the email - i.e. A.
But, if the mail is about group work that everyone should see and has no personal elements, then there is little to fear. It was probably just an oversight.