Paper  doi  bibtex   

@article{ainsworth_functions_1999,
	title = {The functions of multiple representations},
	volume = {33},
	issn = {03601315},
	url = {http://linkinghub.elsevier.com/retrieve/pii/S0360131599000299},
	doi = {10.1016/S0360-1315(99)00029-9},
	number = {2-3},
	journal = {Computers \& Education},
	author = {Ainsworth, Shaaron},
	month = sep,
	year = {1999},
	pages = {131--152}
}