APA

Van Ek J A, Trim J J M, . (1991). Threshold level 1990. Strasbourg: Council of Europe.

Chicago

Van Ek J A, Trim J J M, . 1991. Threshold level 1990. Strasbourg: Council of Europe.

Harvard

Van Ek J A, Trim J J M, . (1991). Threshold level 1990. Strasbourg: Council of Europe.

MLA

Van Ek J A, Trim J J M, . Threshold level 1990. Strasbourg: Council of Europe. 1991.