(1) Is #1 acceptable? Is it natural?
(2) Is #3 acceptable?
(3) How should I correct #5?
1. The Wang family went hiking in the mountains by car last Sunday.
2. The Wang family got in their car and went hiking in the mountains last Sunday.
3. When they arrived there, they saw a lot of bottles, cans, and plastic bags scattered all around the ground.
4. When they arrived there, they saw a lot of bottles, cans, and plastic bags scattered everywhere on the ground.
5. They were really angry to see the mess, so they decided to do their bit for the environmental sanitation.
#1doesn't work for me. It sounds like they went hiking by car, meaning they somehow were hiking with their cars.
#3 is acceptable to me, although I'd prefer to leave off 'the ground'. However, that's more of a stylistic choice, rather than a grammatical error.
#5 is also acceptable as written, although 'environmental sanitation' sounds a bit unnatural. I'd probably just say something like "do their bit for the environment by picking up the trash"
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