甲、乙两化工厂分布如图所示，箭头代表水流方向，如果在a处取水样检测，水中含有少量NaOH、Na₂SO₄；在c处取水样检测，pH=7且水中只含有少量NaCl．则b处水中含有的一组物质是（　　）

—He _______ be here just now. His coffee is still warm.

阅读下面这首诗，完成后面的题。
                                                                                                      十五夜望月
                                                                                                           王建
                                                                                        中庭地白树栖鸦，冷露无声湿桂花。
                                                                                        今夜月明人尽望，不知秋思落谁家。