以下句子，强调的主题是研究者的活动的是（）。

A.ThecausesofLidendriteformationinLi-metalbatterywereinvestigatedbyJones.

B.ThecausesofLidendriteformationinLi-metalbatteryhavenbeenwidelyinvestigated.

C.TherehavebeenseveralinvestigationsintothecausesofLidendriteformationinLi-metalbattery.

D.SomeresearcheshavestudiedthecausesofLidendriteformationinLi-metalbattery.

正确答案：ThecausesofLidendriteformationinLi-metalbatterywereinvestigatedbyJones.