In 1987 sinusitis was the most common chronic medical condition in the United States, followed by arthritis and high blood pressure, in that order. The incidence rates for both arthritis and high blood pressure increase with age, but the incidence rate for sinusitis is the same for people of all ages. The average age of the United States population will increase between 1987 and 2000.
Which of the following conclusions can be most properly drawn about chronic medical conditions in the United States from the information given above

A．Sinusitis will be more common than either arthritis or high blood pressure in 2000.

B．Arthritis will be the most common chronic medical condition in 2000.

C．The average age of people suffering from sinusitis will increase between 1987 and 2000.

D．Fewer people will suffer from sinusitis in 2000 than suffered from it in 1987.

E．(E) A majority of the population will suffer from at least one of the medical conditions mentioned above by the year 20O0.

某一由盐酸、碳酸钠溶液、稀硫酸、氯化铜溶液四种物质中的两种混合形成的混合溶液，现向该混合溶液中滴入氢氧化钡溶液，产生沉淀的质量与加入氢氧化钡溶液体积的关系如图所示．

据此回答：（1）该混合溶液是由______和______组成的．

（2）混合溶液中不含______理由是______

混合溶液中不含______理由是______．