Here are two very similar(in the sense that both test the same thing) SC questions, one form OG verbal and other from the veritas prep test.
OG: The energy source on the Voyager 2 is not nuclear
reactor,in which atoms are actively broken apart;
rather a kind of nuclear battery that uses natural
radioactive decay to produce power
A apart; rather(using a semicolon results in a sentence fragment)
B apart, but rather(correct)
Veritas: Machines powered by hydraulics are not driven by the steam
produced by boiling water, but rather high-pressure fluids
are transmitted throughout the machine to various motors and hydraulic cylinders.
A water, but rather(here but rather is incorrect because of BUT)
B water; instead (correct. semicolon connects two independent clauses)
Now, I understand that in the first question we have a dependent clause, therefore we should not use semicolon and in the second question semicolon connects two independent clauses. However, I don't understand why but rather is incorrect in the veritas question while it is correct in the OG question.
OG: The energy source on the Voyager 2 is not nuclear
reactor,in which atoms are actively broken apart;
rather a kind of nuclear battery that uses natural
radioactive decay to produce power
A apart; rather(using a semicolon results in a sentence fragment)
B apart, but rather(correct)
Veritas: Machines powered by hydraulics are not driven by the steam
produced by boiling water, but rather high-pressure fluids
are transmitted throughout the machine to various motors and hydraulic cylinders.
A water, but rather(here but rather is incorrect because of BUT)
B water; instead (correct. semicolon connects two independent clauses)
Now, I understand that in the first question we have a dependent clause, therefore we should not use semicolon and in the second question semicolon connects two independent clauses. However, I don't understand why but rather is incorrect in the veritas question while it is correct in the OG question.
