'A' seems really similar to C. What exactly in the wording of A do you see as different from C? Is it that you think the 'tendency to and struggle with sin' is too strong of a statement?
Last question first... No, the language re: struggle, etc., is fine to me.
First question, re: wording of 'A', which reads:
A. One nature ( the new one ) plus a tendency to and struggle against sin. The old (flesh) nature is completely dead and no longer exists in the Christian.
I do not believe that the 'old nature', i.e., the propensity to sin is completely dead
. For if that were so, then why would a Christian sin? There would be no source from which sin would be committed. (cf. Matt 15:19; Mk 7:21-23; Rom 7:18) Thus, the new nature though now the predominant 'force' which governs the Christian's thoughts, words and deeds, there still remains part of the old nature from which sin flows. Sanctification is therefore an ongoing and progressive transformation which is accomplished by both the Christian as he/she grows in grace and by the work of the indwelling Spirit. (Phil 2:12,13) It is my understanding that Romans 7 is an autobiographical sketch of Paul's own life, both before and after conversion. The latter consisting of the 'war' that goes on within the one nature; renewed in regeneration yet with a remnant of the sin nature still active.
So again, ONE nature with two opposing predispositions and the new spiritual life created in regeneration having the dominant influence along with the guidance of the Holy Spirit.