（）．

A (2，+∞) B (1，2) C (<img src="https://www.beizhujiaoyu.com/uploads/202208/162139347747951.png" width="20" height="52" />，1) D (0，<img src="https://www.beizhujiaoyu.com/uploads/202208/162139350421581.png" width="20" height="52" />)

A y=x+sin x B y=x²+sin x C y=x+sin<img src="https://www.beizhujiaoyu.com/uploads/202208/162139349992271.png" width="20" height="52" /> D y=x²+sin<img src="https://www.beizhujiaoyu.com/uploads/202208/162139358956381.png" width="20" height="52" />

A 当f’(x)≥0时，f(x)≥g(x) B 当f'(x)≥0时，f(x)≤g(x) C 当f”(x)≥0时，f(x)≥g(x) D 当f”(x)≥0时，f(x)≤g(x)

A 1 B <img src="https://www.beizhujiaoyu.com/uploads/202208/16213935402821.png" width="20" height="52" /> C <img src="https://www.beizhujiaoyu.com/uploads/202208/162139354553111.png" width="20" height="52" /> D <img src="https://www.beizhujiaoyu.com/uploads/202208/162139355363681.png" width="19" height="52" />

A u(x，y)的最大值和最小值都在D的边界上取得 B u(x，y)的最大值和最小值都在D的内部取得 C u(x，y)的最大值在D的内部取得，最小值在D的边界上取得 D u(x，y)的最小值在D的内部取得，最大值在D的边界上取得

A (ad—bc)² B -(ad—bc)² C a²d²-b²c² D b²c²-a²d²

A 必要非充分条件 B 充分非必要条件 C 充分必要条件 D 既非充分也非必要条件