How do I thank the firm that I have been working part time for, when they have reimbursed my expenses for?

visiting their firm two states away? should I send a card, flowers, gift basket, email? I don't know.
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Write a letter...or if it's going to a group a card..short note. That is sufficient! And very thoughtful! If you are hoping for more work a gift basket of food is nice...I've had vendors do this for my employees.
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