A:若p:∃x∈R,x2﹣x+1≥0,则¬p:∀x∈R,x2﹣x+1<0
B:“ sinθ=12 ”是“θ=30°或θ=150°”的充分不必要条件
C:命题“若a=0,则ab=0”的否命题是“若a≠0,则ab≠0”
D:已知p:∃x∈R,cosx=1,q:∀x∈R,x2﹣x+2>0,则“p∧(¬q)”为假命题
Reading is a good habit, but the problem is there's too much to read these days and too little time to read every word of it. There are hundreds of skills to help you read more in less time. Here are two skills that I think are especially good. Preview — if it's long and hard. Previewing is especially useful for getting a general idea of heavy reading like long magazine articles and business reports. Here's how to preview. Read the first two paragraphs and the last two paragraphs carefully. Then read only the first sentence of the other paragraphs. Previewing doesn't give you all the details. It keeps you from spending time on things you don't really want - or need - or read. Skim - if it's short and simple. Skimming is a good way to get a general idea of light reading like popular magazines or the sports and entertainment of your daily paper. Here's how to skim. Get your eyes to move fast. Sweep them across each line. Pick up only a few key words in each line. Everybody skims differently. You and I may not pick up the same words when we skim the same piece, but we'll get a similar idea of what it's all about.
据新华社伦敦5月12日电:英国女王伊丽莎白二世任命保守党领袖卡梅伦为首相,并授权他组建新一届政府。伊丽莎白二世虽然是英国国家的象征,却不掌握国家的最高权力,这种政治制度源于( )