— Will you be able to come and help us clean the room? 

— ______, but I'm doing my homework. [ ]

A. I'd love to

B. I hope not

C. I do care

D. I'm afraid not

已部分变质的Ca(OH)₂固体试样10g，与足量稀盐酸反应，产生2．2gCO₂，则该固体试样中Ca(OH)₂的质量分数为

A．30％

B．40％

C．50％

D．60％