- www.punctilious.org/grammar/sv_agr.htm
- http://owl.english.purdue.edu/owl/resource/599/01/
- http://grammar.ccc.commnet.edu/grammar/cgi.../sv_agr_quiz.htm
- www.bic-englishlearning.com/Subjectverb%5B1%5D.pdf
- http://a4esl.org/q/h/9901/cw-svagreement.html
- www.english-the-easy-way.com/.../Auxiliary_Verbs.htm
- www.writingcentre.uottawa.ca/hypergrammar/auxvb.html
- www.yindii.com/ref/grammar/auxiliary.htm
- http://esl.about.com/library/quiz/bl_auxiliary.htm
- www.krujaroon.com/grammars/.../37%20Auxillary%20verbs.pdf
- www.englishpage.com/modals/modalintro.html
- http://english-language.webpark.pl/modal_verbs.html
- www.brighthub.com/education/languages/.../37641.aspx
- www.autoenglish.org/modalverbs.htm
- www.edu.ge.ch/cptic/prospective/projets/.../intromodal.html
- http://www.youtube.com/watch?v=S5Drs2UuB2Y
- http://www.youtube.com/watch?v=0COmUBQmzeg
