diff --git a/ebook/02.5.md b/ebook/02.5.md
index 5e66b181..39412f2f 100644
--- a/ebook/02.5.md
+++ b/ebook/02.5.md
@@ -160,8 +160,8 @@ method的语法如下：
 		v := 0.00
 		k := Color(WHITE)
 		for _, b := range bl {
-			if b.Volume() > v {
-				v = b.Volume()
+			if bv := b.Volume(); bv > v {
+				v = bv
 				k = b.color
 			}
 		}