Question

1. We need to cut 20 trees to make every 1 ton of paper cups.

1-2. We need to cut 20 trees to make every 1 t of paper cups.

2. We need 10 l of water to make a piece of A4 paper.

3. We need 10 liter of water to make a piece of A4 paper.

4. We need 10 liters of water to make a piece of A4 paper.
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Would you check the sentences? Which expressions do we have to use?

Answer 1

#1 - we spell out numerals below 11, so spell out "one"
#1-2 - We spell "ton," so one is correct in that regard.
#2 - again, I would spell out "liters."
#3 - Ten should be spelled out, and ten is more than one, so it should be "liters."
#4 - Spell out ten.

Note: If you abbreviate "ton" and "liter," it's not totally wrong, but "t" and "l" should have a period: "t."