Father（）the city of New York three days ago. A: leave B: left to C: left off D: left for

“____ he have left yesterday?” Yes, he ____<br/>yesterday.” No, he ____ yesterday.” A: Must; must have left; can’t have left B: Can; can have<br/>left; can’t have left C: Can; must have left; can’t have left D: May; must<br/>have left; shouldn’t have left

It’s quite late now and Mr. While ______ hasn’t left his office. A: still B: already C: since D: yet

求函数$y = \arccos (4x)$的定义域( )。 A: $\left[ { - {1 \over 4},{1 \over 4}} \right]$ B: $\left[ { - 1,1} \right]$ C: $\left[ {0,1} \right]$ D: $\left[ { - 4,4} \right]$

函数\(z = {\left( {xy} \right)^x}\)的全微分为 A: \(dz = \left( { { {\left( {xy} \right)}^x} + \ln xy} \right)dx + x{\left( {xy} \right)^x}dy\) B: \(dz = \left( { { {\left( {xy} \right)}^x} + \ln xy} \right)dx + { { x { { \left( {xy} \right)}^x}} \over y}dy\) C: \(dz = {\left( {xy} \right)^x}\ln xydx + { { x { { \left( {xy} \right)}^x}} \over y}dy\) D: \(dz = {\left( {xy} \right)^x}\left( {1 + \ln xy} \right)dx + { { x { { \left( {xy} \right)}^x}} \over y}dy\)