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I have no idea what your teacher wants for this but here goes something.
C atom has 4 valence electrons, each H atom has two and the oxygen has 6 valence electrons for a total of 12 electrons. In H2C=O, C shares 2 electrons with EACH H atom, and four electrons with the oxygen atom. So there is a single bond between C and each H atom and a double bond between C and O. Said another way, C has four bonds (1 each with H and 2 with O). You can Google "Lewis electron dot structure of formaldehyde" and draw that. As I've described above you will use 12 electrons. For whatever it's worth, if I were teaching the class you could talk all day using words to describe the bonding but if you couldn't draw the Lewis electron dot structure I would not give any credit. Have a great new year.