— I didn't see you yesterday.
— ______ I was ill yesterday, ______ I didn't go to work.
A:Because; so
B:For; and
C:/; but
D:/; so
实验室用硝酸钾配制50.0g溶质的质量分数为20%的硝酸钾溶液,下列说法正确的是( )
①体温恒定 ②变温动物 ③胎生、哺乳 ④体表被毛 ⑤属于先天性行为 ⑥属于学习行为