Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

          I am sure you have heard about global warming. Global warming may make the sea level become higher. Do you know why? It is because global wanning causes the earth to be warmer and this in turn makes glaciers melt.

          What is a glacier? It is a large sheet of ice that moves very, very slowly. Some melting glaciers add more water to the ocean. Higher temperatures also make water expand. When water expands in the ocean, it takes up more space and the level of the sea rises.

          Coastal flooding could cause salt water to flow into areas where salt is harmful, threatening plants and animals in those areas. Leaders of all nations around the world are in the fight against global warming but "change only happens when individuals take action.

Global warming may make the level of the sea become _____.