diff --git a/.travis.yml b/.travis.yml
index f52bbce..38a4c85 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,14 +1,12 @@
 language: node_js
 node_js:
-  - "6"
+  - "10"
 
 addons:
   chrome: stable
 
-before_script:
-  - "export DISPLAY=:99.0"
-  - "sh -e /etc/init.d/xvfb start"
-  - sleep 3 # give xvfb some time to start
+services:
+  - xvfb
 
 before_install:
   npm install karma-cli -g
\ No newline at end of file
diff --git a/quz/quz.js b/quz/quz.js
index 624e7de..ac01409 100755
--- a/quz/quz.js
+++ b/quz/quz.js
@@ -9,6 +9,12 @@
  */
 function dcate(A, B) {
 	/** Fill in here **/
+	let currList = A
+	while (currList.tail !== null) {
+		currList = currList.tail;
+	}
+	currList.tail = B;
+	return A;
 }
 
 /**
@@ -24,4 +30,18 @@ function dcate(A, B) {
  */
 function sub(L, start, len) {
 	/** Fill in here **/
+	if (!L || !(/(^[0-9]\d*$)/.test(start)) || !(/(^[0-9]\d*$)/.test(len))) throw new Error('param error');
+	let newList = [],
+		subLen = 0,
+		currList = L,
+		currIndex = 0
+	do {
+		if (currIndex >= start){
+			newList.push(currList.head);
+			subLen++;
+		}
+		currList = currList.tail;
+		currIndex++;
+	} while (len !== subLen && currList !== null);	
+	return new List.list(newList);
 }