S1. Roseate is an adjective for the rose flower. S2. The rose is a powerful poetic symbol in many languages. The second statement:

The first statement gives a factual/linguistic note about the adjective 'roseate' referring to the rose. The second statement moves beyond this linguistic point to discuss the rose as a poetic symbol across languages. This broadens the scope of discussion from a single adjective to the cultural-poetic significance of the rose. Thus, the second 'expands' the topic introduced by the first rather than explaining it (explicates), opposing it (contrasts), or duplicating it (coincides). Therefore (a) expands the first is the correct answer.