Explanation

Squaring a : b : c : d = √4 : √3 : √2 : √1 gives a² : b² : c² : d² = 4 : 3 : 2 : 1, so write a² = 4k², b² = 3k², c² = 2k², d² = k². The numerator becomes −4k² + 3k² + 2k² + k² = 2k² and the denominator 4k² − 3k² + 2k² − k² = 2k². Their ratio is 2k²/2k² = 1, which is option (a).