本题考查当代凯尔特语中占主导地位的语言。
Among the contemporary Celtic languages Welsh is the strongest: about one-fifth of the total population of Wales are able to speak it.
在当代凯尔特语中，威尔士语占据主导地位：大约有五分之一的威尔士人会说威尔士语。
故选择A选项。