Definition: In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.
Input: Question: Is the country that Slater traveled to with Thomas Carter an island? Passage:In 1874 he accompanied the botanist Isaac Bayley Balfour and George Gulliver aboard HMS Shearwater on an expedition to observe the transit of Venus on Rodrigues. In addition to studies of the flora and fauna, Slater excavated the subfossil bones of extinct birds, including the Rodrigues solitaire (Pezophaps solitaria) and Rodrigues starling (Necropsar rodericanus). His records were used by the zoologists Albert Günther and Alfred Newton to write the first scientific description of the Rodrigues starling in 1879. During a stay in Mauritius in 1875 he and George Gulliver explored the flora, the herpetofauna, and the aquatic avifauna. In 1885 he traveled with Thomas Carter to Iceland. Based partly on his work there, he wrote the Manual of the Birds of Iceland, published in 1901. In 1897 Slater described the short-tailed parrotbill (Paradoxornis davidianus) and the sulphur-breasted warbler (Phylloscopus ricketti). Together with William Bernhardt Tegetmeier and Frederick William Frohawk, he wrote the fifth volume of British Birds With Their Nests and Eggs (1898). In 1877 Slater was elected a Fellow of the Zoological Society of London (FZS). He was also a member of the British Ornithologists' Union.
 Links: a. Iceland b. Frederick William Frohawk c. British Ornithologists' Union d. Rosario-class sloop
Output:
a