下列合并同类项：①3x-2y=1；②x2+x2=x4；③3mn-3mn=0；④4ab2-5ab2=-ab2；⑤3m2+4m3=7m5．其中错误的有（ ）
A．4个
B．3个
C．2个
D．1个
∵3x和-2y不能合并，∴①错误；
∵x2+x2=2x2，∴②错误；
∵3mn-3mn=0，∴③正确；
∵4ab2-5ab2=-ab2，∴④正确；
∵3m2和4m3∴⑤错误；
∴正确的有2个，错误的有3个，
故选B．
| 完形填空。 | ||||
| Chang'e I, China's pioneering lunar probing (月球探测) satellite, came through its first lunar eclipse (月食) yesterday and had regained full operations. The moon orbiter was temporarily hidden from solar rays and lost 1 with Earth for two-and -half hours during a blackout that started at 10 a.m., Ye Peijian, chief commander and designer in 2 of the satellite system, said. Chang'e I had to switch off some its 3 and rely on onboard batteries during this challenging time, when it was 4 from solar energy, Ye said. Full details of how Chang'e I 5 during the eclipse were due to be released last night. Gu Shen, a deputy (副) director with the lunar probe's measurement and control system, said scientists 6 the orbit of the satellite and shortened the 7 the probe was out of direct sunlight by about 80 minutes. As of 10 pm. Wednesday, the satellite had 8 1204 orbits of the moon.Before yesterday's eclipse, the 9 time Chang's I had been without contact with the Earth was 49 minutes. The European Space Agency helped 10 the satellite, which will perform a second orbital adjustment during another eclipse in August, Ye said. | ||||
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