Practise exercises

Explanations a- the- no article:
http://www.edufind.com/english/grammar/DETERMINERS2.cfm

Exercises:

http://www.englisch-hilfen.de/en/exercises/nouns_articles/article_a2.htm

Exercises gerunds vs infinitives

http://www.ego4u.com/en/cram-up/grammar/infinitive-gerund/exercises?04

http://www.ego4u.com/en/cram-up/grammar/infinitive-gerund/exercises?05