diff --git a/【实践课内】3.选择结构2/7-1 选择-星期.c b/【实践课内】3.选择结构2/7-1 选择-星期.c
new file mode 100644
index 0000000..76a0659
--- /dev/null
+++ b/【实践课内】3.选择结构2/7-1 选择-星期.c	
@@ -0,0 +1,29 @@
+#include <stdio.h>
+
+int main() {
+    int n;
+
+    scanf("%d", &n);
+
+    n %= 7;
+
+    if (n == 0) {
+        printf("Friday\n");
+    } else if (n == 1) {
+        printf("Saturday\n");
+    } else if (n == 2) {
+        printf("Sunday\n");
+    } else if (n == 3) {
+        printf("Monday\n");
+    } else if (n == 4) {
+        printf("Tuesday\n");
+    } else if (n == 5) {
+        printf("Wednesday\n");
+    } else if (n == 6) {
+        printf("Thursday\n");
+    } else {  // Wrong input
+        printf("What're you doing?\n");
+    }
+
+    return 0;
+}
diff --git a/【实践课内】3.选择结构2/7-1 选择-星期.jpg b/【实践课内】3.选择结构2/7-1 选择-星期.jpg
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diff --git a/【实践课内】3.选择结构2/7-2 21选择-我们是冠军.c b/【实践课内】3.选择结构2/7-2 21选择-我们是冠军.c
new file mode 100644
index 0000000..058a162
--- /dev/null
+++ b/【实践课内】3.选择结构2/7-2 21选择-我们是冠军.c	
@@ -0,0 +1,52 @@
+#include <stdio.h>
+
+int main() {
+    int type;
+    double s1, s2, s3;
+
+    scanf("%d%lf%lf%lf", &type, &s1, &s2, &s3);
+
+    if (type == 0) {  // 赛跑，从低到高排序
+        if (s1 > s2) {
+            double temp = s1;
+            s1 = s2;
+            s2 = temp;
+        }
+
+        if (s1 > s3) {
+            double temp = s1;
+            s1 = s3;
+            s3 = temp;
+        }
+
+        if (s2 > s3) {
+            double temp = s2;
+            s2 = s3;
+            s3 = temp;
+        }
+
+        printf("%.2lf %.2lf %.2lf\n", s1, s2, s3);
+    } else {  // type == 1
+        if (s1 < s2) {
+            double temp = s1;
+            s1 = s2;
+            s2 = temp;
+        }
+
+        if (s1 < s3) {
+            double temp = s1;
+            s1 = s3;
+            s3 = temp;
+        }
+
+        if (s2 < s3) {
+            double temp = s2;
+            s2 = s3;
+            s3 = temp;
+        }
+
+        printf("%.2lf %.2lf %.2lf\n", s1, s2, s3);
+    }
+
+    return 0;
+}
diff --git a/【实践课内】3.选择结构2/7-2 21选择-我们是冠军.jpg b/【实践课内】3.选择结构2/7-2 21选择-我们是冠军.jpg
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diff --git a/【实践课内】3.选择结构2/7-3 21选择-盘闰年.c b/【实践课内】3.选择结构2/7-3 21选择-盘闰年.c
new file mode 100644
index 0000000..3821de4
--- /dev/null
+++ b/【实践课内】3.选择结构2/7-3 21选择-盘闰年.c	
@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int main() {
+    int n;
+
+    scanf("%d", &n);
+
+    // 判断闰年
+    if ((n % 4 == 0 && n % 100 != 0) || n % 400 == 0) {
+        // 判断是否含 4
+        if (n % 10 == 4 || n / 10 % 10 == 4 || n / 100 % 10 == 4 || n / 1000 % 10 == 4) {
+            printf("panta!\n");
+        } else {
+            printf("1\n");
+        }
+    } else {
+        printf("0\n");
+    }
+
+    return 0;
+}
diff --git a/【实践课内】3.选择结构2/7-3 21选择-盘闰年.jpg b/【实践课内】3.选择结构2/7-3 21选择-盘闰年.jpg
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diff --git a/【实践课内】3.选择结构2/7-4 选择-合法日期.c b/【实践课内】3.选择结构2/7-4 选择-合法日期.c
new file mode 100644
index 0000000..8ca0ca8
--- /dev/null
+++ b/【实践课内】3.选择结构2/7-4 选择-合法日期.c	
@@ -0,0 +1,39 @@
+#include <stdio.h>
+
+int main() {
+    int y, m, d;
+
+    scanf("%4d/%2d/%2d", &y, &m, &d);
+
+    if (m < 1 || m > 12 || d < 1) {
+        printf("No\n");
+    } else if (m == 1 || m == 3 || m == 5 || m == 7 || m == 8 || m == 10 || m == 12) {
+        if (d <= 31) {
+            printf("Yes\n");
+        } else {
+            printf("No\n");
+        }
+    } else if (m == 2) {
+        if (y % 4 == 0 && y % 100 != 0 || y % 400 == 0) {
+            if (d <= 29) {
+                printf("Yes\n");
+            } else {
+                printf("No\n");
+            }
+        } else {
+            if (d <= 28) {
+                printf("Yes\n");
+            } else {
+                printf("No\n");
+            }
+        }
+    } else {  // m == 4 || m == 6 || m == 9 || m == 11
+        if (d <= 30) {
+            printf("Yes\n");
+        } else {
+            printf("No\n");
+        }
+    }
+
+    return 0;
+}
diff --git a/【实践课内】3.选择结构2/7-4 选择-合法日期.jpg b/【实践课内】3.选择结构2/7-4 选择-合法日期.jpg
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