题干
In the past decade, our education system too much on grades. However, grades have a direct connection with future success is still a question.
A：focused; whether
B：focused; if
C：has focused; whether
D：has focused; if
答案(点此获取答案解析）
C
着人们生活节奏的加快，方便的小包装食品已被广泛接受，为了延长食品的保质期，防止食品受潮及富脂食品氧化变质，在包装袋中应放入的化学物质是