diff --git a/problems/0235.二叉搜索树的最近公共祖先.md b/problems/0235.二叉搜索树的最近公共祖先.md
index b7e92e4e..b27a231e 100644
--- a/problems/0235.二叉搜索树的最近公共祖先.md
+++ b/problems/0235.二叉搜索树的最近公共祖先.md
@@ -513,6 +513,31 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 递归
+public TreeNode LowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
+{
+    if (root.val > p.val && root.val > q.val)
+        return LowestCommonAncestor(root.left, p, q);
+    if (root.val < p.val && root.val < q.val)
+        return LowestCommonAncestor(root.right, p, q);
+    return root;
+}
+// 迭代
+public TreeNode LowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
+{
+    while (root != null)
+    {
+        if (root.val > p.val && root.val > q.val)
+            root = root.left;
+        else if (root.val < p.val && root.val < q.val)
+            root = root.right;
+        else return root;
+    }
+    return null;
+}
+```
 
 
 <p align="center">
diff --git a/problems/0669.修剪二叉搜索树.md b/problems/0669.修剪二叉搜索树.md
index 00186558..229a2ab1 100644
--- a/problems/0669.修剪二叉搜索树.md
+++ b/problems/0669.修剪二叉搜索树.md
@@ -567,6 +567,23 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 递归
+public TreeNode TrimBST(TreeNode root, int low, int high)
+{
+    if (root == null) return null;
+    if (root.val < low)
+        return TrimBST(root.right, low, high);
+
+    if (root.val > high)
+        return TrimBST(root.left, low, high);
+
+    root.left = TrimBST(root.left, low, high);
+    root.right = TrimBST(root.right, low, high);
+    return root;
+}
+```
 
 
 <p align="center">
diff --git a/problems/0701.二叉搜索树中的插入操作.md b/problems/0701.二叉搜索树中的插入操作.md
index 265bbb5b..98e60d5f 100644
--- a/problems/0701.二叉搜索树中的插入操作.md
+++ b/problems/0701.二叉搜索树中的插入操作.md
@@ -691,6 +691,17 @@ impl Solution {
     }
 }
 ```
+### C#
+``` C#
+// 递归
+public TreeNode InsertIntoBST(TreeNode root, int val) {
+    if (root == null) return new TreeNode(val);
+
+    if (root.val > val) root.left = InsertIntoBST(root.left, val);
+    if (root.val < val) root.right = InsertIntoBST(root.right, val);
+    return root;
+}
+```
 
 
 <p align="center">