Students are asked to keep the school clean and tidy.Litter baskets have been placed in the school,but students still throw rubbish everywhere.

• 都是被动语态，为什么“学生们已被告知要保持校园的整洁”用一般时，而“废物筐都已被设置在了校园里”用现在完成？都用一般时或都用现在完成行吗？谢谢