题干
There is ________ “u” and ________ “h” in the word “hour”.
A：a; a
B：an; an
C：a; an
D：an; a
答案(点此获取答案解析）
C
There is ________ “u” and ________ “h” in the word “hour”.
A：a; a
B：an; an
C：a; an
D：an; a
2NH3（g） △H=－92．4 kJ/mol