Concord (subject-verb agreement) practice
• http://www.ccc.commnet.edu/grammar/quizzes/svagr2.htm
• https://www.llas.ac.uk/materialsbank/mb061/8.4/5a.htm
• http://www.eslflow.com/Subject-verbagreement.html
• http://www.grammarbook.com/grammar_quiz/subject_verb_agreem
ent_1.asp
• http://a4esl.org/q/j/kf/mc-svad.html