Can anyone pls suggest what ‘They’ is referring to in option ‘C’?

Thanks in advance.

The Middle Stone Age, extended for 200,000 years from 300,000 BC TO 500,000 BC, is marked by the intelligent manufacture by the tribals of glues used for fixing honed heads to the spears and arrows, a complex process that, in the absence empirical means of observation, requires far more abstract perception than modern technology


(A) extended for 200,000 years from 300,000 BC TO 500,000 BC, is marked by the intelligent manufacture by the tribals of glues used for fixing honed heads to the spears and arrows, a complex process that, in the absence empirical means of observation, requires far more mental and abstract perception than

(B) was extended for 200,000 years from 300,000 BC TO 500,000 BC, marked by the intelligent manufacture by the tribal of glues used for fixing honed heads to the spears and arrows, a complex process that, in the absence empirical means of observation, required far more mental and abstract perception than

(C) extended for 200,000 years from 300,000 BC TO 500,000 BC, was marked by the intelligent manufacture by the tribals of glues which they used for fixing honed heads to the spears and arrows, a complex process that, in the absence empirical means of observation, required far more mental and abstract perception than

(D) extending for 200,000 years from 300,000 BC TO 500,000 BC, and marked by the intelligent manufacture by the tribals of glues used for fixing honed heads to the spears and arrows, a complex process that in the absence empirical means of observation, requires far more mental and abstract perception than

(E) extended for 200,000 years from 300,000 BC TO 500,000 BC, was marked by the intelligent manufacture by the tribals of glues used for fixing honed heads to the spears and arrows, a complex process that, in the absence empirical means of observation, required far more mental and abstract perception than does


Diagnostic Verbal Test No. 5 Q# 13 SC