Sentence:  The staminate willow catkins , then , provide their visitors with both nectar and pollen ; a marvelous arrangement , for it provides exactly what the bee queens need to make their beebread , a <WSD>combination</WSD> of honey and pollen with which the young of all species are fed . 
Meaning of the word marked with <WSD> tags:  a collection of things that have been combined; an assemblage of separate parts or qualities