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Direction for Question: You have a passage followed by questions based on it. Read the passage carefully and choose the best answer to each question out of the four alternatives.

Recent technological advancement in manned and unmanned undersea vehicles overcome some of the limitations of diver's equipment. Without a vehicle, divers often became sluggish and their mental concentration was limited because of undersea pressure that affected their mind concentration. But today, most oceanographers make observations by means of instruments that are lowered into the ocean or from samples taken from the water. Direct observations of the ocean floor are made not only by the divers, but also by deep submarines. Radio equipped buoys can be operated by remote control in order to transmit information back to land based laboratories including data about water temperature, currents and weather. Some of mankind's most serious problems, especially those concerning energy and food may be solved with the help of observations made possible by these undersea vehicles.

With what topic is this passage primarily concerned?                     

A)  Recent technological advances.

B)  Communication among divers.

C)  Undersea vehicles.

D)  Direct observation of the ocean floor.