My sweater is long（变为否定句）.The yellow bag is ￥15.（便一般疑问句）.Are his pants blue?（做否定回答）.That apple is 《green》（对书名号里的提问）.Those long rulers are 《20 yuan》（对书名号里的提问）

My sweater is long（变为否定句)
My sweater is NOT long.
The yellow bag is ￥15.（便一般疑问句）
Is the yellow bag ￥15?
Are his pants blue？（做否定回答）。
No,it isn't.
That apple is 《green》（对书名号里的提问）。
what color is the apple?
Those long rulers are 《20 yuan》（对书名号里的提问）
How much is those long rulers?

My sweater is long（变为否定句)
My sweater is not long.
否定句一般就是在be动词（is am are）后加上表示否定意义的not,或者是和助动词一起使用,比如：don't/doesn't.
The yellow bag is ￥15.（便一般疑问句）
Is the yellow bag ￥15?
一般疑问句就是将be动词提到句首,其余部分按陈述句语序排列即可.
Are his pants blue?（做否定回答）
No, they aren't.
肯定回答是Yes,they are.
That apple is 《green》（对书名号里的提问）
What's the color of that apple?
题目要求对颜色进行提问,即是“什么颜色的意思”,用英语表达便是What's the color of +要问颜色的物品
Those long rulers are 《20 yuan》（对书名号里的提问）
How much of those long rulers?
问价格是用how much,而且不管是单数还是复数,一律用how much.