Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. Possibly due to some explosion about five billion years ago, this nebular cloud began to collapse, causing gravitational contractions as its particles interacted. B. About five billion years ago, a supernova may have exploded, causing a huge cloud of gases and heavier elements to form C. Gravitational attraction among particles of gases and heavier elements caused some explosive event nearly five billion years ago. D. About five billion years ago, a shock wave from an external event caused this huge cloud of gases to collapse into small grains of heavier elements.