题干
The maths problem is very easy, so I can work it out ________.
A：in trouble
B：without difficulty
C：by heart
D：with your help
答案(点此获取答案解析）
B
The maths problem is very easy, so I can work it out ________.
A：in trouble
B：without difficulty
C：by heart
D：with your help
X+2CO2，X的化学式为（ ）