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.