下列四种形式的循环设计中，循环次数最少的是______。

A：a = 5 : b = 8
Do
 a = a + 1
Loop While a < b

B：a = 5 : b = 8
Do
 a = a + 1
Loop Until a < b

C：a = 5 : b = 8
Do Until a < b
 b = b + 1
Loop

D：a = 5 : b = 8
Do Until a > b
 a = a + 1
Loop