an expert team --- to study h7n9 bird flu virus in april 2013a\ is set upb\ was set upc\ HAS SET UP请您说明理由好吗?

an expert team --- to study h7n9 bird flu virus in april 2013a\ is set upb\ was set upc\ HAS SET UP请您说明理由好吗?
an expert team --- to study h7n9 bird flu virus in april 2013
a\ is set up
b\ was set up
c\ HAS SET UP
请您说明理由好吗?

an expert team --- to study h7n9 bird flu virus in april 2013a\ is set upb\ was set upc\ HAS SET UP请您说明理由好吗?
选B,研究团队是被组建,且时间在april 2013,表示发生在该文章完成之前.C的话要改为has been set up也是正确的