My baseball is under the table.（对under the table<br/>提问）<br/>My math book is on the desk.(改为一般疑问句)<br/>They are some good dictionaries.（改为单数句）<br/>Under the bed is a red ruler.（改为同义句）

【答案】
My baseball is under the table.（对under the table 提问）
under the table是地点 --> Where is your basketball?
你的篮球在哪儿?
My math book is on the desk.(改为一般疑问句)
助动词提前 --> Is your math book on the desk?
你的数学书[是不是]在桌面上?
They are some good dictionaries.（改为单数句）
it is a good dictionary. 这是一本好的词典.
Under the bed is a red ruler.（改为同义句）
a red ruler is under the bed. 倒装句顺过来变成主谓顺序.
有一把红色的尺子在床底下.
【其他答案】
Where is your baseball?
Is your math book on the desk ?
It is a good dictionary .
There is a red ruler under the bed .
Where is my baseball?
Is my math book on the desk?
This is a good dictionaries.
The red ruler is under the bed.