Sentence:  The present study focuses on the acquisition of a specific verbal element, namely the <WSD>copula</WSD>, in predicative constructions in a cross-linguistic perspective (English, German, Croatian). 
Meaning of the word marked with <WSD> tags:  A word, usually a verb, used to link the subject of a sentence with a predicate (usually a subject complement or an adverbial), that unites or associates the subject with the predicate.