Hi,
I received a PM to respond to this one. So here goes my analysis.
The period when the great painted caves at Lascaux and Altamira were occupied by Upper Paleaolithic peoples
has been established by carbon dating, but what is much more difficult to determine are the use to which primitive peoples put the caves, the reason for their decoration, and the meaning of the magnificently depicted animals.
Since the meaning of this sentence is very straight-forward, let me directly get to the error analysis of this question.
Error Analysis: The only error in this sentence is the SV number agreement error in the IC that begins after comma + FANBOYS. The subject of the IC after but is “what is much more difficult to determine”. This subject is a dependent clause. Whenever a clause or a phrase acts as a subject of a clause, it is always singular. So we have a singular subject here. But the verb for this subject is “are”, which is plural in number. Hence we have SV number agreement error here. This verb should be “is”.
PoE:A. has been established by carbon dating, but what is much more difficult to determine are:
Incorrect for the reason stated above.
B. have been established by carbon dating, but what is much more difficult to determine are:
Incorrect.1. Repeats the same SV number agreement error as in A.
2. Subject “The period” is singular and the verb used for it is plural “have been established”. We have another SV number agreement error here.
C. have been established by carbon dating, but that which is much more difficult to determine is:
Incorrect. 1. Repeats the “have been established” SV error as in choice B.
2. Use of “that which” is incorrect as comma + FANBOYS should be followed by an IC.
D. has been established by carbon dating, but what is much more difficult to determine is:
Correct. This choice rectifies the error of choice A.
E. are established by carbon dating, but that which is much more difficult to determine is: Incorrect.
Incorrect 1. Plural verb “are” does not agree in number with singular subject “The period”.
2. Repeats the comma + FANBOYS error as in choice C.
Hope this helps.
Thanks.
Shraddha