I am collecting the documents

I am a self-employed dentist and since my arrival to the UK (over 7.5 years ago) I have been working for 2 different dental practices as an associate. I do not trade as a limited company and do not own any of the businesses!
I am now lost with :
3. Evidence that the business is/was actively trading
At least two of the following:
copies of invoices for services provided
contracts to provide services
receipts for purchase of tools or business equipment
testimonials or references from clients, with their contact details (note: we will verfy these
documents)
examples of business advertising (such as flyers, online advertising, listing in Yellow Pages,
listing in trade magazines or on trade websites)
any other relevant evidence.
-So firstly, they mean "at least two" per year I guess ?
-Any suggestions to what to enclose, as I do not trade directly as a business!
"Actively" trading .... I get every month a payment from the practice I work at, but I will be including that as "Proof of earnings from self-employed"
Many thanks
Max