在上个世纪下半叶，神经网络迅速地发展起来了。

A.Neural networks are developed rapidly in the second half of the last century.

B.Neural networks have been developed rapidly in the second half of the last century.

C.Neural networks were developed rapidly in the second half of the last century.

D.Neural networks had been developed rapidly in the second half of the last century.

正确答案：Neural networks were developed rapidly in the second half of the last century.