The bohr model of an atom shows a nucleus with electrons circling around it. what does the bohr model show that makes it a useful model for understanding atoms?

differences in sizes of electrons and protons
distances of the electrons from the nucleus
number of electrons in each orbital
paths of the electrons around the nucleus

Combustion is the act or process of burning. therefore, i believe the answer is  a: burning wood. 

Vander waals forces are inter molecular bonds that exist within molecules of the same substance. a water molecule is made up of oxygen and hydrogen atoms which share electrons between each other. the vander waals forces are forces that exist between multitude of different  molecules of water. dipole dipole forces is the type of vander waals force that exist in water. the oxygen atom which is more electronegative pulls the shared electron closer to itself thus generating a partial negative charge while the hydrogen acquire a partial positive charge. these two different charges causes attraction to occur in water molecules.