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"My friend told me there was something in the box, but I didn't know what it was yet. "

"The key functions of a refrigerator are to keep food cold and prevent spoilage. "

"The teacher's narration of the historical event helped the students understand the causes of the war. "

"Many medications are derivatives of natural substances found in plants or fungi. "

"The noisy environment of the school cafeteria made it difficult to concentrate on my homework. "

"The United States is in an awkward situation with debt default looming."

"My teacher explained the new math formula specifically for students in the advanced class. "

"My concentration was high during the important math test. "

"Words cannot express the love I feel for him."

"The complicated instructions on the new software difficult me from completing the project on time. "

"The beginning of the school year is always exciting. "

"In the sentence, "This book is mine," the word "this" is a demonstrative that points to a specific noun. "