**(D) 40 : 25**

Consider the given ratios, 2 : 3, 5 : 8, 75 : 121 and 40 : 25.

Simplified form of 2: 3 = 2/3 = 0.67

Simplified form of 5 : 8 = 5/8 = 0.625

Simplified form of 75: 121 = 75/121 = 0.61

Simplified form of 40: 25 = 40/25 = 1.6

**Therefore, the greatest ratio among the given ratios is 40 : 25**