4.若x,y满足$\left\{\begin{array}{l}x+y≥0\\ x≥1\\ x-y≥0\end{array}\right.$则下列不等式恒成立的是( )
A. | y≥1 | B. | x≥2 | C. | x+2y+2≥0 | D. | 2x-y+1≥0 |
3.抛物线x2=4y上的点到其焦点的最短距离为( )
A. | 4 | B. | 2 | C. | 1 | D. | $\frac{1}{2}$ |
2.设集合A={x∈R|x>1},B={x∈R|x2≤4},则A∪B=( )
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A. | [-2,+∞) | B. | (1,+∞) | C. | (1,2] | D. | (-∞,+∞) |