diff --git a/【额外练习】选择结构/7-1 选择-孔融让梨.c b/【额外练习】选择结构/7-1 选择-孔融让梨.c
new file mode 100644
index 0000000..b71b18e
--- /dev/null
+++ b/【额外练习】选择结构/7-1 选择-孔融让梨.c	
@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int main() {
+    int a, b;
+
+    scanf("%d%d", &a, &b);
+
+    if (a < b) {
+        printf("%d\n", a);
+    } else {
+        printf("%d\n", b);
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-1 选择-孔融让梨.jpg b/【额外练习】选择结构/7-1 选择-孔融让梨.jpg
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diff --git a/【额外练习】选择结构/7-2 选择-奇偶判断.c b/【额外练习】选择结构/7-2 选择-奇偶判断.c
new file mode 100644
index 0000000..0588bac
--- /dev/null
+++ b/【额外练习】选择结构/7-2 选择-奇偶判断.c	
@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int main() {
+    int a;
+
+    scanf("%d", &a);
+
+    if (a % 2 == 1) {
+        printf("YES\n");
+    } else {
+        printf("NO\n");
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-2 选择-奇偶判断.jpg b/【额外练习】选择结构/7-2 选择-奇偶判断.jpg
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diff --git a/【额外练习】选择结构/7-3 选择-ASCII值.c b/【额外练习】选择结构/7-3 选择-ASCII值.c
new file mode 100644
index 0000000..59a9984
--- /dev/null
+++ b/【额外练习】选择结构/7-3 选择-ASCII值.c	
@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int main() {
+    char c;
+
+    scanf("%c", &c);
+
+    if ('0' <= c && c <= '9') {
+        printf("%d\n", c);
+    } else {
+        printf("input error\n");
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-3 选择-ASCII值.jpg b/【额外练习】选择结构/7-3 选择-ASCII值.jpg
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index 0000000..532a549
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diff --git a/【额外练习】选择结构/7-4 选择-闰年.c b/【额外练习】选择结构/7-4 选择-闰年.c
new file mode 100644
index 0000000..b9ce518
--- /dev/null
+++ b/【额外练习】选择结构/7-4 选择-闰年.c	
@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int main() {
+    int year;
+
+    scanf("%d", &year);
+
+    if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
+        printf("YES\n");
+    } else {
+        printf("NO\n");
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-4 选择-闰年.jpg b/【额外练习】选择结构/7-4 选择-闰年.jpg
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index 0000000..167bca5
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diff --git a/【额外练习】选择结构/7-5 选择-排序.c b/【额外练习】选择结构/7-5 选择-排序.c
new file mode 100644
index 0000000..6ff353d
--- /dev/null
+++ b/【额外练习】选择结构/7-5 选择-排序.c	
@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int main() {
+    double a, b;
+
+    scanf("%lf%lf", &a, &b);
+
+    if (a > b) {
+        printf("%.3lf %.3lf\n", a, b);
+    } else {
+        printf("%.3lf %.3lf\n", b, a);
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-5 选择-排序.jpg b/【额外练习】选择结构/7-5 选择-排序.jpg
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diff --git a/【额外练习】选择结构/7-6 选择-分段函数3.c b/【额外练习】选择结构/7-6 选择-分段函数3.c
new file mode 100644
index 0000000..b46b343
--- /dev/null
+++ b/【额外练习】选择结构/7-6 选择-分段函数3.c	
@@ -0,0 +1,18 @@
+#include <math.h>
+#include <stdio.h>
+
+int main() {
+    double x;
+
+    scanf("%lf", &x);
+
+    if (x < 1) {
+        printf("%.3lf\n", x);
+    } else if (1 <= x && x < 10) {
+        printf("%.3lf\n", sqrt(x * 2 - 1));
+    } else {  // x >= 10
+        printf("%.3lf\n", log(x * 3 - 11));
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-6 选择-分段函数3.jpg b/【额外练习】选择结构/7-6 选择-分段函数3.jpg
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diff --git a/【额外练习】选择结构/7-7 选择-圆塔.c b/【额外练习】选择结构/7-7 选择-圆塔.c
new file mode 100644
index 0000000..8d7d440
--- /dev/null
+++ b/【额外练习】选择结构/7-7 选择-圆塔.c	
@@ -0,0 +1,18 @@
+#include <stdio.h>
+
+int main() {
+    double x, y;
+
+    scanf("%lf%lf", &x, &y);
+
+    if ((x - 2) * (x - 2) + (y - 2) * (y - 2) <= 1
+        || (x + 2) * (x + 2) + (y - 2) * (y - 2) <= 1
+        || (x + 2) * (x + 2) + (y + 2) * (y + 2) <= 1
+        || (x - 2) * (x - 2) + (y + 2) * (y + 2) <= 1) {
+        printf("10\n");
+    } else {
+        printf("0\n");
+    }
+
+    return 0;
+}
diff --git a/【额外练习】选择结构/7-7 选择-圆塔.jpg b/【额外练习】选择结构/7-7 选择-圆塔.jpg
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