Single choice ( 2 points per question, 30%)(一)1. When 0.20molL-1 NaOH standard solution was used to titrate the mixtures of 0.10 molL-1H2SO4 and 0.10molL-1H3PO4, _end points could be observed on the titration curves. ( )A. 1 B. 2 C. 3 D. 42. Which one of the following is a pair of conjugate acid and base? ( ) A. H2CO3CO32- B. HPO42-PO43- C. H3PO4HPO42- D. NH3-NH3.H2O3. The solubility of Ag2S in