Kobashi,
Thank you so much for your reply.
Yes, I tried to look at my website on different devices. I know my background image is not responsive, and I also do not know how to fix it. So, I uploaded a new background image!
But same problem!! This new image is responsive, but the white space between menu and header image, and the space between the image and the footer are still there.
I think it is not the problem of the image.