First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the text, which is the mantle of the Earth. It is a general statement that does not need any other sentence for context. It does not use any pronouns or definite articles that refer to previous information. Why other lines are not chosen? Paragraph 2 starts with "The rocks" which uses a definite article and refers to something specific, so it is not independent. Paragraph 3 starts with "Common silicates" which also uses a definite article and is not independent. Paragraph 4 starts with "The other major type" which uses a definite article and is not independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it adds a final detail about the types of rocks in the mantle. It does not introduce new ideas but wraps up the information about the mantle.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives more details about the mantle. It explains what the mantle is made of, which is a logical flow from the general statement about the mantle.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it gives specific examples of the silicates mentioned in Paragraph 2. This shows a progression from a general statement to specific details.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it introduces another type of rock found in the mantle. This shows a logical order by adding more information about the rocks in the mantle.