Read the following passage and choose the correct answer to each of the questions.

Recent technological advances in manned and unmanned vehicles, along with breakthroughs in satellite technology and computer equipment, have overcome some of the limitations of divers and diving equipment for scientists doing research on the great oceans of the world. Without a vehicle, divers often became sluggish, and their mental concentration was severely limited. Because undersea pressure affects their speech organs, communication among divers has always been difficult or impossible. But today, most oceanographers avoid the use of vulnerable human divers, preferring to reduce the risk to human life and make direct obervations by means of instruments that are lowered into the ocean, from samples take from the water, or from photographs made by orbiting satellites. Direct observations of the ocean floor can be made not only by divers but also by deep-diving submarines in the water and even by the technology of sophisticated aerial photgraphy from vantage points above the surface of more than seven miles and cruise at depths of fifteen thousand feet. In addition, radio-equipped buoys can be operated by remote control in order to transmit data back to land-based laboratories via satellite. Particularly important for ocean study are data about water temperature, currents, and weather. Satellite photographs can show the distribution of sea ice, oil slicks, and cloud formations over the ocean. Maps created from satellite pictures can represent the temperature and the color of the ocean’s surface, enabling researchers to study the ocean currents from laboratories on dry land. Furthermore, computers help oceanographers to collect, organize, and analyze data from submarines and satellites. By creating a model of the ocean’s movement and characteristics, scientists can predict the patterns and possible effects of the ocean on the enviroment. Recently, many oceanographers have been relying more on satellites and computers than on research ships or even submarine vehicles because they can supply a greater range of information more quickly and more effectively. Some of humankind’s most serious problems, especially those concerning energy and food, may be solved with the help of observations made possible by this new technology.

The word “sluggish” is closest in meaning to A. very weak B. nervous C. slow moving D. confused