同时应用加法交换律、结合律的是[ ]
A.49-18+51= 49+51-18
B.a+b+c= a+(b+c)
C.256+137+44=137+(256+44)
答案:C
I'm busy now. I'm sorry I can't help ____ the flowers.
A.watering
B.watered
C.waters
D.to water
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