@@ -744,11 +744,11 @@ class Airplane {
 getCruisingAltitude() {
 switch (this.type) {
 case '777':
-return getMaxAltitude() - getPassengerCount();
+return this.getMaxAltitude() - this.getPassengerCount();
 case 'Air Force One':
-return getMaxAltitude();
+return this.getMaxAltitude();
 case 'Cessna':
-return getMaxAltitude() - getFuelExpenditure();
+return this.getMaxAltitude() - this.getFuelExpenditure();
 }
 }
 }
@@ -763,21 +763,21 @@ class Airplane {
 class Boeing777 extends Airplane {
 // ...
 getCruisingAltitude() {
-return getMaxAltitude() - getPassengerCount();
+return this.getMaxAltitude() - this.getPassengerCount();
 }
 }
 
 class AirForceOne extends Airplane {
 // ...
 getCruisingAltitude() {
-return getMaxAltitude();
+return this.getMaxAltitude();
 }
 }
 
 class Cessna extends Airplane {
 // ...
 getCruisingAltitude() {
-return getMaxAltitude() - getFuelExpenditure();
+return this.getMaxAltitude() - this.getFuelExpenditure();
 }
 }
 ```
@@ -1009,12 +1009,12 @@ class UserSettings {
 }
 
 changeSettings(settings) {
-if (this.verifyCredentials(user)) {
+if (this.verifyCredentials()) {
 // ...
 }
 }
 
-verifyCredentials(user) {
+verifyCredentials() {
 // ...
 }
 }
@@ -1410,35 +1410,35 @@ classes until you find yourself needing larger and more complex objects.
 **Bad:**
 ```javascript
 const Animal = function(age) {
-if (!(this instanceof Animal)) {
-throw new Error("Instantiate Animal with `new`");
-}
+if (!(this instanceof Animal)) {
+throw new Error("Instantiate Animal with `new`");
+}
 
-this.age = age;
+this.age = age;
 };
 
 Animal..move = function() {};
 
 const Mammal = function(age, furColor) {
-if (!(this instanceof Mammal)) {
-throw new Error("Instantiate Mammal with `new`");
-}
+if (!(this instanceof Mammal)) {
+throw new Error("Instantiate Mammal with `new`");
+}
 
-Animal.call(this, age);
-this.furColor = furColor;
+Animal.call(this, age);
+this.furColor = furColor;
 };
 
 Mammal. = Object.create(Animal.);
 Mammal..constructor = Mammal;
 Mammal..liveBirth = function() {};
 
 const Human = function(age, furColor, languageSpoken) {
-if (!(this instanceof Human)) {
-throw new Error("Instantiate Human with `new`");
-}
+if (!(this instanceof Human)) {
+throw new Error("Instantiate Human with `new`");
+}
 
-Mammal.call(this, age, furColor);
-this.languageSpoken = languageSpoken;
+Mammal.call(this, age, furColor);
+this.languageSpoken = languageSpoken;
 };
 
 Human. = Object.create(Mammal.);
@@ -1449,29 +1449,29 @@ Human..speak = function() {};
 **Good:**
 ```javascript
 class Animal {
-constructor(age) {
-this.age = age;
-}
+constructor(age) {
+this.age = age;
+}
 
-move() {}
+move() { /* ... */ }
 }
 
 class Mammal extends Animal {
-constructor(age, furColor) {
-super(age);
-this.furColor = furColor;
-}
+constructor(age, furColor) {
+super(age);
+this.furColor = furColor;
+}
 
-liveBirth() {}
+liveBirth() { /* ... */ }
 }
 
 class Human extends Mammal {
-constructor(age, furColor, languageSpoken) {
-super(age, furColor);
-this.languageSpoken = languageSpoken;
-}
+constructor(age, furColor, languageSpoken) {
+super(age, furColor);
+this.languageSpoken = languageSpoken;
+}
 
-speak() {}
+speak() { /* ... */ }
 }
 ```
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