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What One Adds to the Other is a free printable Grade 4 English worksheet on identifying what a second text supplies, aligned to Common Core standard RI.4.9. It prints 2 questions with an answer key on its own sheet of paper, in 25 versions, 23 of them with different questions, so no two pupils in the class work from the same page. Print it from the browser or download it as a PDF — no account, no email.

Set 25 of 25 · the same problems every time you open this link.

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Set 1 has all 25 in a single PDF. 23 of these 25 sets ask different questions — this skill does not have 25 questions to give. The rest reorder them, so no two pupils have the same paper in front of them.

What One Adds to the Other

RI.4.9

NameDate

Read the text, then answer the questions.

1.Read the text, then answer the questions.

What a Coral Reef Is

A coral reef looks like rock and is built by animals. A coral polyp is a soft creature the size of a pinhead. It draws calcium from the sea water and builds a hard cup around itself. Millions of polyps, cup upon cup, become a reef. Inside each polyp live tiny algae. The algae make food from sunlight and pass most of it to the polyp. In exchange they get shelter and the polyp's waste. Neither could build a reef alone. When the water gets too warm, the polyps expel the algae. Without them the coral turns white and starves. That is what bleaching means. A reef takes centuries to build and can bleach in a single hot summer.

  1. 1. How is the coral partnership like the one in a lichen?
  2. 2. How is a reef different from a rock?
2.Read the text, then answer the questions.

The Accidental Photograph

In 1895 Wilhelm Röntgen was working with a covered tube in a darkened room when he noticed a screen across the laboratory glowing. Something was passing through the cover and crossing the room. He did not know what it was, so he called it X — the unknown. He spent seven weeks alone in the laboratory testing it. He put wood, rubber and metal in the way. Metal stopped it; the rest did not. Then he asked his wife to put her hand between the tube and a photographic plate. The picture showed the bones of her hand and her wedding ring. Within a year, X-rays were being used in hospitals. Röntgen refused to patent them.

  1. 1. How did the two discoveries differ in what happened next?
  2. 2. How is this discovery like penicillin's?

LessonPrint · RI.4.9 · Set 25 · free to copy for classroom use

Answer key — What One Adds to the Other

Set 25. Prints on its own sheet.

  1. 1.1. Both are two organisms living together where each supplies what the other cannot make. 2. A reef looks like rock but is built by living animals, cup upon cup.
  2. 2.1. X-rays reached hospitals within a year; penicillin took sixteen years and two more scientists. 2. Both began with somebody noticing something unexpected that they had not set out to find.

Last reviewed 2026-09-05. Aligned to RI.4.9 of the Common Core State Standards for English language arts.