Choose the correct answers that, where, this, what

Read and choose the best option  to complete the passage.

The warming of the Pacific Ocean has created weather patterns (41)______ strongly affect the world. When the water is warm, the (42)______ of rainfall in Indonesia and the surrounding regions decreases. Australia could (43)______ experience a drought in many parts. On (44)______ hand, Chile (which borders the Pacific Ocean) is preparing for (45)______ rainstorms. In Pakistan and northwestern India, the weather pattern makes the rainy season weaker and makes the area much drier. This happening is called El Nino and is used (46)______ weather forecasters to make long-range weather predictions. They also know that El Nino will (47)______ unusually heavy rains to the southwestern part of the United States and make the central part of the country drier at the same time. According to research, weather forecasters (48)______ know about the coming weather with certainty. Now everything has become completely different. El Nino itself used to be (49)______. It would occur every two to seven years. But now, this weather pattern is becoming more frequent. We cannot say when and how often tornadoes or cyclones(lốc xoáy) occur. Scientists are unsure of the reason for this (50)______ on a global scale either

• A. that
• B. what
• C. when
• D. whether