室温下，甲溶液中水电离出的H⁺浓度为10^-12 mol•L^-1，乙溶液中水电离出的H⁺浓度为10^-2 mol•L^-1，下列说法中正确的是（　　）

A．甲、乙两溶液的pH不可能相同

B．甲、乙两种溶液中加入Al粉都会产生H₂

C．HCO₃^- 不可能在甲、乙两溶液中大量共存

D．甲不可能是盐溶液，乙不可能是酸或碱溶液

It’s all annual back-to-school routine. One morning you wave goodbye, and that (1) evening you’re burning the late-night oil in sympathy. In the race to improve educational standards, (2) are throwing the books at kids. (3) elementary school students are complaining of homework (4) What’s a well-meaning parent to do.As hard as (5) may he, sit back and chill, experts advise. Though you’ve got to get them to do it, (6) helping too much, or even examining (7) too carefully, you may keep them (8) doing it by themselves. "I wouldn’t advise a parent to check every (9) assignment," says psychologist John Rosemond, author of Ending the Tough Homework. "There’s a (10) of appreciation for trial and error. Let your children (11) the grade they deserve. " Many experts believe parents should gently look over the work of younger children and ask them to rethink their (12) . But "you don’t want them to feel it has to be (13) ," she says.

That’s not to say parents should (14) homework-first, they should monitor how much homework their kids (15) . Thirty minutes a day in the early elementary years and an hour in (16) four, five, and six is standard, says Rosemond. For junior-high students it should be " (17) more than an hour and a half," and two for high school students. If your child (18) has more homework than this, you may want to check (19) other parents and then talk to the teacher about (20) assignments.

17（）

A.about

B.no

C.much

D.few