diff --git a/.gitignore b/.gitignore
index b512c09..3091757 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-node_modules
\ No newline at end of file
+node_modules
+coverage
\ No newline at end of file
diff --git a/.travis.yml b/.travis.yml
index f52bbce..aafbc82 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,10 +4,11 @@ node_js:
 
 addons:
   chrome: stable
+services:
+  - xvfb
 
 before_script:
   - "export DISPLAY=:99.0"
-  - "sh -e /etc/init.d/xvfb start"
   - sleep 3 # give xvfb some time to start
 
 before_install:
diff --git a/karma.conf.js b/karma.conf.js
index 0747749..f829f0d 100644
--- a/karma.conf.js
+++ b/karma.conf.js
@@ -30,13 +30,17 @@ module.exports = function(config) {
     // preprocess matching files before serving them to the browser
     // available preprocessors: https://npmjs.org/browse/keyword/karma-preprocessor
     preprocessors: {
+      'quz/*.js': ['coverage']
+    },
+    coverageReporter: {
+      type : 'html',
+      dir : 'coverage/'
     },
-
 
     // test results reporter to use
     // possible values: 'dots', 'progress'
     // available reporters: https://npmjs.org/browse/keyword/karma-reporter
-    reporters: ['progress'],
+    reporters: ['progress', 'coverage'],
 
 
     // web server port
diff --git a/package.json b/package.json
index e80646a..895ecd0 100644
--- a/package.json
+++ b/package.json
@@ -20,8 +20,9 @@
   },
   "homepage": "https://github.com/FE-star/homework1#readme",
   "devDependencies": {
-    "karma": "^1.7.0",
+    "karma": "^1.7.1",
     "karma-chrome-launcher": "^2.2.0",
+    "karma-coverage": "^1.1.2",
     "karma-mocha": "^1.3.0",
     "mocha": "^3.5.0",
     "should": "^11.2.1"
diff --git a/quz/quz.js b/quz/quz.js
index 624e7de..f088b77 100755
--- a/quz/quz.js
+++ b/quz/quz.js
@@ -8,7 +8,16 @@
  * @returns {List}
  */
 function dcate(A, B) {
-	/** Fill in here **/
+  function getListLast (list) {
+    if (!list.tail) {
+      return list
+    } else {
+      return getListLast(list.tail)
+    }
+  }
+  let lastA = getListLast(A)
+  lastA.tail = B
+  return A
 }
 
 /**
@@ -23,5 +32,19 @@ function dcate(A, B) {
  * @returns {List}
  */
 function sub(L, start, len) {
-	/** Fill in here **/
+  if (!L || (!start && start !== 0) || (!len && len !== 0)) {
+    throw new Error('缺少参数')
+  }
+	function getListByIndex (list, index, from = 0) {
+    if (from === index) {
+      return list
+    } else {
+      from ++
+      return list.tail && getListByIndex(list.tail, index, from)
+    }
+  }
+  let startList = getListByIndex(L, start)
+  let endList = getListByIndex(startList, (start + len - 1), start)
+  endList && (endList.tail = null)
+  return startList
 }
diff --git a/test/test.js b/test/test.js
index 317a346..a1a7f6d 100755
--- a/test/test.js
+++ b/test/test.js
@@ -16,6 +16,9 @@ describe('unit test for quz.js', function () {
         it('should get the sublist consisting of LEN items from list L', function () {
         	C.toString().should.equal('[ 19 8 7 3 2 ]');
             sub(C, 3, 2).toString().should.equal('[ 3 2 ]');
+            should.throws(() => sub(C, 3), function (err) {
+              return err.message.includes('缺少参数')
+            });
             C.toString().should.equal('[ 19 8 7 3 2 ]');
         });
     });