某居民6.8买入1000美元，以7.0卖出，则收益率为（ ）%，赚（ ）元。 A: 2.94；200 B: 2.94；300 C: 2.857；325 D: 2.857；225

设分块矩阵 [tex=8.714x2.857]bDwiEQkgsQNmlfJDfwyldqA6UJUpdqH3CfgSVhSew6UZORRZCFLRoxNxDyC6tCW1EMYijhaXnVLzJq7qvc+34SrktT7JvZZX6HLm5EaCt0j1sqw3Wdf11hQfCQuQflw/JJxmQvdC6QSpTci93/gjZhUFPaqPcXjPP//4a5XQrPKqnRmVPgn2BydeF6JugmL7[/tex],其中 [tex=0.929x1.0]zkuxy59wnc0FrSuUc1OFF6pw7am5S+IP5AAfiovVsGI=[/tex] 是 [tex=2.286x1.143]FxpPcmjsncQgkXunitg21Q==[/tex] 的可逆矩阵,证明:[tex=12.929x2.786]TIwZYBkNsy31H1RNd/OloEMAfDxZAX4PiGFnDh43Vq40QIi3RzyCoT+MVtAv/z+Tqnmh03zUVNJC/Aj1Vl4Ch6kjdxwYXuVUklm0bzMl+LkYosi8/gy10SS7n1/SV7L0yPvomGoKcm39sYhEu2elCYi+f71Kr1K2vzUbBRo9dvG4Thpuleq2ey1KB1GhJqxzyem43/GT/zYLELAFAsYouV5YbO6gboiFQ/y3sy6pEoIbIibvwsVHO+RzLl0JzV91[/tex]。

设分块矩阵 [tex=8.714x2.857]bDwiEQkgsQNmlfJDfwyldqA6UJUpdqH3CfgSVhSew6UZORRZCFLRoxNxDyC6tCW1EMYijhaXnVLzJq7qvc+34SrktT7JvZZX6HLm5EaCt0j1sqw3Wdf11hQfCQuQflw/JJxmQvdC6QSpTci93/gjZhUFPaqPcXjPP//4a5XQrPKqnRmVPgn2BydeF6JugmL7[/tex],其中 [tex=0.929x1.0]zkuxy59wnc0FrSuUc1OFF6pw7am5S+IP5AAfiovVsGI=[/tex] 是 [tex=2.286x1.143]FxpPcmjsncQgkXunitg21Q==[/tex] 的可逆矩阵,证明:[tex=12.929x2.786]TIwZYBkNsy31H1RNd/OloEMAfDxZAX4PiGFnDh43Vq40QIi3RzyCoT+MVtAv/z+Tqnmh03zUVNJC/Aj1Vl4Ch6kjdxwYXuVUklm0bzMl+LkYosi8/gy10SS7n1/SV7L0yPvomGoKcm39sYhEu2elCYi+f71Kr1K2vzUbBRo9dvG4Thpuleq2ey1KB1GhJqxzyem43/GT/zYLELAFAsYouV5YbO6gboiFQ/y3sy6pEoIbIibvwsVHO+RzLl0JzV91[/tex]。

设分块矩阵 [tex=8.714x2.857]bDwiEQkgsQNmlfJDfwyldqA6UJUpdqH3CfgSVhSew6UZORRZCFLRoxNxDyC6tCW1EMYijhaXnVLzJq7qvc+34SrktT7JvZZX6HLm5EaCt0j1sqw3Wdf11hQfCQuQflw/JJxmQvdC6QSpTci93/gjZhUFPaqPcXjPP//4a5XQrPKqnRmVPgn2BydeF6JugmL7[/tex],其中 [tex=0.929x1.0]zkuxy59wnc0FrSuUc1OFF6pw7am5S+IP5AAfiovVsGI=[/tex] 是 [tex=2.286x1.143]FxpPcmjsncQgkXunitg21Q==[/tex] 的可逆矩阵,证明:[tex=12.929x2.786]TIwZYBkNsy31H1RNd/OloEMAfDxZAX4PiGFnDh43Vq40QIi3RzyCoT+MVtAv/z+Tqnmh03zUVNJC/Aj1Vl4Ch6kjdxwYXuVUklm0bzMl+LkYosi8/gy10SS7n1/SV7L0yPvomGoKcm39sYhEu2elCYi+f71Kr1K2vzUbBRo9dvG4Thpuleq2ey1KB1GhJqxzyem43/GT/zYLELAFAsYouV5YbO6gboiFQ/y3sy6pEoIbIibvwsVHO+RzLl0JzV91[/tex]。

设分块矩阵 [tex=8.714x2.857]bDwiEQkgsQNmlfJDfwyldqA6UJUpdqH3CfgSVhSew6UZORRZCFLRoxNxDyC6tCW1EMYijhaXnVLzJq7qvc+34SrktT7JvZZX6HLm5EaCt0j1sqw3Wdf11hQfCQuQflw/JJxmQvdC6QSpTci93/gjZhUFPaqPcXjPP//4a5XQrPKqnRmVPgn2BydeF6JugmL7[/tex],其中 [tex=0.929x1.0]zkuxy59wnc0FrSuUc1OFF6pw7am5S+IP5AAfiovVsGI=[/tex] 是 [tex=2.286x1.143]FxpPcmjsncQgkXunitg21Q==[/tex] 的可逆矩阵,证明:若 [tex=4.429x1.214]8cRFT1Hfou4GkkcgYUW2S3ZSIes72KpWMtM4NlpjZYUCwVotB5TbZ552rlYuhVWX[/tex] 则[tex=10.286x2.786]TIwZYBkNsy31H1RNd/OloEMAfDxZAX4PiGFnDh43Vq40QIi3RzyCoT+MVtAv/z+Tqnmh03zUVNJC/Aj1Vl4Ch6kjdxwYXuVUklm0bzMl+LkYosi8/gy10SS7n1/SV7L0yPvomGoKcm39sYhEu2elCffV6KaN5ud1QT2eahh+dHvYE0n4OL+iZy/wq85/piRI+YoKxrSLtt3HvD0rAz2+Bw==[/tex]。

下列变量组（）是一个闭回路。 A: {x，x，x，x，x，x} B: {x，x，x，x，x} C: {x，x，x，x，x，x} D: {x，x，x，x，x，x}

以下谓词蕴含式正确的是（）: (∀x) (A(x)→B(x))=>( ∀x)A(x)→(∀x)B(x)|(∀x) (A(x)↔B(x))=>( ∀x)A(x)↔(∀x)B(x)|(∀x)A(x)∨(∀x)B(x)=>( ∀x) (A(x)∨B(x))|(∃x) (A(x)∧B(x))=>(∃x)A(x)∧(∃x)B(x)

以下谓词蕴含式正确的是（）: (?x) (A(x)→B(x))=>( ?x)A(x)→(?x)B(x)|(?x) (A(x)?B(x))=>( ?x)A(x)?(?x)B(x)|(?x)A(x)∨(?x)B(x)=>( ?x) (A(x)∨B(x))|(?x) (A(x)∧B(x))=>(?x)A(x)∧(?x)B(x)

下列式中错误的是： A: (∀x)(A(x)Úp(x)) Û (∀x)A(x)Ú (∀x)p(x) B: ($x)A(x) Ù p Û ($x)(A(x) Ù p ) C: (∀x)(A(x)ÚB(x)) Þ (∀x)A(x)Ú( ∀x)B(x) D: ($x)(A(x)ÙB(x)) Þ ($x)A(x)Ù( $x)B(x)

东方公司欲购进一台新机器，要支付400万元，该机器的使用寿命为四年，无残值，如果采用直线法计提折旧，预计每年可产生税前利润40万元，如果所得税税率为30%，则静态投资回收期为（）年。 A: 2.5 B: 2.857 C: 3.12 D: 4