A:8
B:10
C:30
D:93
①2CO ②2N ③ Cu+2O ④2Na+⑤Mg2+⑥H2O.
Mary come to our party,but she isn't very sure.
—What do you think of a house supplied by Lovell?
— you buy a home from Lovell,the company promises to buy it back at the same price after three years.