Detailed Instructions: You are given a paragraph, with numbered sentences, and a question. Write the numbers of the sentences needed to answer the given question. Separate multiple sentence numbers with a comma (", "). E.g. "1, 2" would be the correct response if Sent 1 and Sent 2 are needed to answer the given question (do not include sentences that contain no information that is necessary to answer the question). Sort the sentence numbers in an increasing order (i.e., '1, 2', instead of '2, 1'). Your answer should not contain anything than the sentence numbers separated by a comma (e.g. '1, 2, 3, 4'). The given question requires more than one sentence to answer. So, your answer must contain at least one comma (", ").
Problem:Paragraph- Sent 1: Like flowing water, flowing ice erodes the land.
Sent 2: It also can deposit the material elsewhere.
Sent 3: Glaciers cause erosion in two main ways: plucking and abrasion.
Sent 4: Plucking is caused when sediments are picked up by a glacier.
Sent 5: They freeze to the bottom of the glacier and are carried away by the flowing ice.
Sent 6: Abrasion occurs when glaciers scrape over the Earths surface.
Sent 7: The ice sheet acts like sandpaper.
Sent 8: The ice contains sediments and rocks frozen in the ice.
Sent 9: The rocks and sediment grind away as the glacier moves.
Sent 10: They wear away rock.
Sent 11: They may also leave scratches and grooves in them.
Sent 12: Scientists use these grooves to learn about the direction the glacier has moved. 
Question: Which kind of erosion acts like sandpaper?.
Solution:
6, 7.