http://www.spca.org.sg/animalwelfare_details.asp?id=134
https://www.1800petmeds.com/education/common-diseases-senior-dog-cat-40.htm
https://www.helpyourdogfightcancer.com/CausesPrevention.shtml
IMAGES:
https://www.google.com.sg/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0ahUKEwi5mJCjrfTWAhUJwI8KHR_bB2IQjhwIBQ&url=https%3A%2F%2Fethology.eu%2Fcan-my-dog-be-happy-or-sad%2F&psig=AOvVaw2fxqkXo_bsy-GQo3w-yZi2&ust=1508216175609592