Central America is a thin, narrow, but long piece of land surrounded by water on two sides, but which is connected to other land masses on both ends - we call such a land an Isthmus, so the correct answer is a).
Other examples of an Isthmus are for example Manila - the capital of the Philippines and the Suez Canal (which is not very long though)
In mountains lava doesn't come out and in volcanoes lava does come out
