Nominal and participle clauses?

I was completing an exercise about nominal and participal clauses where I had to complete the clauses by finding them in the text. In bold are the answers that I had to fill in:

employed by this company

what individuals believe to be proper behaviour

what might be a funny or sarcastic remark in person

describing the content of the email

encouraged in this company

receiving spam or other unwanted messages at work

I do not understand how these are nominal or principal clauses, if someone could please help me