ANSWER: D
5 spiders = 5 flies = 5 minutes
1 spider = 1 fly = 5 minutes
Therefore,
100 spiders = 100 flies = 5 minutes
100 spiders = 100 × 2 flies = 5 × 2 minutes
∴ 100 spiders = 100 × 20 flies = 5 × 20 minutes
= 100 spiders = 2000 flies = 100 minutes