Hi @qing_zhao and welcome to the Canvas Community. You've posted your question to a global community of Canvas users from different institutions where we discuss our experiences so we don't have access to information on the specific Canvas system at your college. For questions about submitting homework, you need to speak to your course teacher or the local technical support team at your college. I can see from your email address that you study at San Jose State University and a quick look at their website tells me you can get technical support here: http://www.sjsu.edu/it/self-service/
Alternatively you could click the "Help" button on the left of the screen when you're in Canvas, where you should see a link to "Ask your instructor a question". This will let you contact the course teacher. Good luck in finding an answer and submitting your work!
