With or Without comma and why?

0I was asked to analyse and discuss the following 2 questions but I have little understanding about. Please help.02br
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00Questions # 1 02br
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001. Yesterday I saw a schoolboy.02br
002 He was knocked down by a sppeding car.02br
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00Combibe sentence 1 and sectence 2 to a single sentence and pick the correct answer or answers. Explain the difference between the one or ones you think is or are correct and the one or ones you think is or are wrong in terms of its or their meanings.02br
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00Choices:02br
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00a. Yesterday I saw a school boy who was knocked down by a speeding car.02br
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00b. Yesterday I saw a school boy, who was knocked down by a speeding car.02br
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00c. Yesterday I saw a school boy knocked down by a speeding ca.02br
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00d. Yesterday I saw a school boy, knocked down by a speeding car.02br
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00Questions # 202br
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003. Yesterday I saw the schoolboy.02br
004. He was knocked down by a sppeding car.02br
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00Combibe sentence 3 and sectence 4 to a single sentence and pick the correct answer or answers. Explain the difference between the one or ones you think is or are correct and the one or ones you think is or are wrong in terms of its or their meanings.02br
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00Choices:02br
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00e. Yesterday I saw the school boy who was knocked down by a speeding car.02br
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00f. Yesterday I saw the school boy, who was knocked down by a speeding car.02br
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00g. Yesterday I saw the school boy knocked down by a speeding ca.02br
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00f. Yesterday I saw the school boy, knocked down by a speeding car.0-