请教有关时态的的问题

New techniques in thermal-scanning photography, a process that records radiation from surface areas,makes it possible to study the effects of calefation, or warming ,of a river in greater than ever before.

A.makes it possible to study the effects of calefation, or warming ,of a river in greater than ever before.

B.have made it possible to study in greater detail than ever before the effects of calefaction,or warming ,of a river

为什么选B不选A呢？只是因为时态的问题么？还是与ever before的位置有关？为什么用完成时呢？

对了，你有机会帮我看看我的那道题吧。就是题目为：这道题应该选A吧？

呵呵！~