Read the following passage and mark the letter A, B, C, or D to indicate the answer to each of the question.

Is synchronized swimming really a sport? Despite the doubt of many people, synchronized swimming is one of the most underrated but most difficult sports, and it certainly deserves to be in the Olympic Games.

Olympic synchronized swimmers train for as long as eight hours a day, for six days a week− much longer than most other Olympic sports. The athletes are not just in the water the whole time, they spend hours stretching, doing Pilates, strength conditioning, diligently training, lifting weights, performing ballet, and even dancing and doing gymnastics. Because of this, synchronized swimmers are some of the strongest and skillful athletes to compete in the modern Olympic Games.

Synchronized swimmers must perform many movements and positions called figures while managing their breathing and coordination with the swimmers around them. To increase their lung capacity, often times synchronized swimmers will do exercises called “unders” during practices. They will swim a 25-meter lap underwater, repeating this exercise over and over until they’re beyond exhausted. This exercise is completely necessary for synchronized swimmers to master, because more than half of a routine is performed underwater.

Although synchronized swimming is a very graceful and beautiful sport, there can be some dangers. The synchronized swimmers can’t touch the bottom of the pool in a routine, or they’ll be disqualified. They must continuously move their legs in circular movements, like an egg-beater. Because synchronized swimming is a contact sport and the swimmer’s kicks are so powerful, swimmers may get hit by other competitors’ legs, causing concussions or knocking off nose clips, which is an essential piece of equipment. Since it’s fairly common for a nose clip to get knocked off, many times swimmers will swim with a couple extras.

As mentioned in the passage, what do swimmers have to pay attention in order to have a successful performance?