答案：B
翻译：--谁在操场上打篮球?--是杰瑞.
解释：
1. 对疑问句的回答要遵守“怎么问,怎么答”的对应原则.
2. 楼主只需要想象所谓的对句子划线提问即可.
Jerry is playing basketball on the playground.
如果对Jerry划线提问,则问句刚好就是原题.
3. 而上句中的playing baksetball on the playground部分,因为在问句中已经出现,所以回答时候可以加以省略.
即：Jerry is. = Jerry is (playing baksetball on the playground).
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