I'm wondering if this piece is no. 19 because it is fairly confusing. I am going to call this piece a contrasting period with an extension. I would say it is A-B-b prime. The first phrase is 4 bars long ending with a half cadence. The second phrase starts with the pick-ups to bar 5 and also last 4 bars but ends with a deceptive cadence, thus indicating that the period does not end here (if it is, indeed, a period). The extension is rhythmically the same as the 3rd bar of the second phrase, except a modulation or tonicization of dominant has occurred. The two bar extension ends with a PAC in B major (the piece started in E).