This is a practice sheet that I usually assign as homework but it can be used to supplement a lesson on definite and indefinite articles. I teach my students the general rule using 'DIONA' and 'LONERS'. If a work ends in d, ión, or a, it is usually a feminine word and therefore will need a feminine article. If a word ends in l, o, n, e, r or s (*not a plural s) it is usually a masculine formed word and needs a masculine article. I put in a trick or 2 with words that are plural to see if students are paying attention.