What structure do insects have for breathing (a) gills (b) tracheae (c) skin (d) lungs

True, the standard unit for volume is liters which can be represented by either a lower case "l" or a capital "l"

21 just playing hshsjsjshsgdhdhdhhd

It idk haha what are we doing?

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).