Which choice makes the sentence most grammatically acceptable?
","rationale_html":null,"correct_answer":["C"],"equiv_key":null,"has_media":false,"has_mathml":false,"has_table":false,"section_label":"English","options":[{"label":"A","content_html":"No Change
","ord":0},{"label":"B","content_html":"collapse to form stars.
","ord":1},{"label":"C","content_html":"collapse, stars form.
","ord":2},{"label":"D","content_html":"collapse and form stars.
","ord":3}],"passage":{"id":"act_practice_pdf:pt2:english:p5","source_id":"act_practice_pdf","form_id":"act_practice_pdf:pt2","section":"english","number":"V","kind":null,"title":"A Birthplace of Stars","content_html":"The winter night I attempted to see the famed Orion Nebula, I didn’t expect to succeed. I was an inexperienced astronomer peering through36 light-polluted skies. But I was eager to test my new telescope’s capabilities, and the nebula is said to be one of the greatest sights in the night sky. So I bundled up, set out my scope to cool down (its mirrors must adjust to the cold air for optimal viewing), and scanned for the constellation Orion. I had prepared for this night by studying constellations in my astronomy books. Orion appears as a hunter who, in some mythologies, is fighting Taurus the Bull, another constellation. [ A ] Even in bright skies, the telltale three stars marking Orion’s belt are easy to spot. [ B ] I knew to follow the belt to Orion’s sword, a dim line of stars extending south. [ C ] The middle of these is actually not a star but a nebula, the Great Orion Nebula, a birthplace of stars. [ D ] When gravity causes the gas and dust to collapse, forming stars.37 The nebula, is home to thousands of young stars,38 is often called a galactic “nursery.” G I centered my scope where the nebula should be, inserted my lowest-powered eyepiece, and leaned in to look. I just made out a dull smudge. I couldn’t get much improvement even when I adjusted the focuser. Coincidentally,40 I switched to a higher-powered eyepiece and tried a trick I’d read about for viewing faint objects: using averted vision. The principle of averted vision states that the eye can often see distant objects better by looking to one side of them rather than directly at them. I I focused my eye on an area beside the smudge, and, sure enough, my peripheral vision yielded a far better view of the nebula’s swirling clouds. I even saw the Trapezium star cluster, illuminated42 by four bright young stars nestled in the nebula like birds’ eggs43 in a nest. L
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