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

Global warming is the current increase in temperature of the Earth’s surface (both land and water) as well as its atmosphere. Average temperature around the world have risen by 0.75°C (1.4°F) (13)_____ the last 100 years. About two thirds of this increase has occurred since 1975 in the past, when the Earth experienced increases in temperature it was the result of natural causes, but today it is being caused by accumulation of greenhouse gases in the atmosphere produced by human (14)______. The natural greenhouse effect maintains the Earth’s temperature at a safe level making it (15)_____ for humans and many other life forms to exist. However, since The Industrial Revolution what benefits human has significantly enhanced the greenhouse effect (16)______ the Earth’s average temperature to rise by almost 1°C . This is creating the global warming (17)_____ we see today.