Question

这些英语句子怎么改形式？

this is a piano（改复数）
that knife is short（改复数）
is it a spoon？（改复数）
are they old cooks？（改单数）
are those girls new？（肯定句）
are these pencil-boxes old？（肯定句）

Answer 1

this is a piano（改复数）
These are pianos

that knife is short（改复数）
Those knives are short

is it a spoon？（改复数）
Are they spoons?

are they old cooks？（改单数）
Is he / she an old cook? 楼上朋友错了这题

are those girls new？（肯定句）
Those girls are new. 楼上朋友错了这题

are these pencil-boxes old？（肯定句）
These pencil-boxes are old.

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Answer 2

there are some pianos
those knives are short
are they spoons?
is she/he old cook?
is that girl new？
these pencil-boxes are old