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.

Question: How old was the Finnish Navy when it lost one fifth of its ships? Passage:On 4 May 1918, in the aftermath of the Finnish Civil War, Silatch arrived secretly in Kotka, Finland, to evacuate remaining members of the Finnish Red Guard. However, she was confiscated by the Finns and joined the Finnish icebreaker fleet as Ilmarinen, after the legendary hero from Kalevala. In December 1919 she was sent to Koivisto to assist three Finnish torpedo boats, C1, C2 and C3 that had been surrounded by ice some thick. The 150-ton torpedo boats had participated in the British campaign in the Baltic, and Admiral Walter Cowan had demanded that the Finnish squadron patrolling the area had to stay until the British forces had withdrawn. Despite the efforts of Ilmarinen, the weak-hulled torpedo boats were crushed by the ice, and the newly founded Finnish Navy lost one fifth of its ships. After the winter of 1919 Ilmarinen was laid up until she was returned to the Soviet Union according to the Treaty of Tartu. In turn the Soviets gave back the Finnish icebreaker Avance. The name Ilmarinen was later given to a Finnish coastal defence ship launched in 1931.
Links: a. Apu (1899 icebreaker) b. Finnish Navy c. Finnish Navy d. Kalevala
b