This question is Agree / Disagree question.
Opponents of abiogenic theory claims for nonexistence of CH4 in mantel. So, anything that claims for no CH4 is close to strengthening the opponents.
A) Since the opponents claim for nonexistence of hydrocarbons in mantel, "condensation of hydrocarbons released from the earth's mantel" itself is something he/she would disapprove of. Considering this, claiming oil does not involve that hydrocarbon is something opponents are likely to agree. (Correct)
B) Since the opponent is against abiogenic, it's more likely to embrace organic matter becoming oil than agreeing to "small" amount of organic matter involved in "large" oil reserve. They would more likely to disagree with this statement.
C) This would be weakening because 'diamond theory' is used by advocates.
D) Same as C). High pressure offsetting the temperature is used by advocates.
E) Since opponents claim for no CH4 in mantel, this would weaken it.