题目

用所给词汇的正确形式填空 1．Dick sings ____，she sings ____ than John，but Mary sings ____ in her class.(well) 2．He is ____ at learning math. He is much ____ at Chinese and he is the _____ at English.(bad) 3．Annie says Sally is the ________ (kind) person in the world. 4．The white flower is ________．The yellow flower is ______than the white flower. The red flower is ______ of the three.(beautiful) 5．He is ___________ (clever) than any other boy in the class. 6．Which T-shirt is ______________ (expensive), this red one or that purple one? 7．Tom acted the _____ （10分）在真空中的O点放一点电荷Q=1.0×10-9 C，直线MN过O点，OM=30cm，M点放一点电荷q=C，如图所示。求：（1）M点的电场强度大小；（2）若M、 N两点的电势差为15V，则电荷q从M点移到N点，电势能变化了多少？