题目

如图所示，一木板B放在水平地面上，木块A放在木板B的上面，木块A的右端通过弹簧测力计固定在竖直墙壁上．用力F向左拉木板B，使它以速度v运动，这时木块A静止，弹簧测力计的示数为F．下列说法中正确的是（ ）A. 木板B受到的滑动摩擦力等于FB. 地面受到的滑动摩擦力等于FC. 若木板B以2v的速度运动，木块A受到的滑动摩擦力等于2FD. 若用力2F拉木板B，木块A受到的滑动摩擦力等于FWhen I was growing up, I always gave my mom an apron （围裙）on her birthday．I wanted my own mom —   21  that apron I'd just given her, of course —to   22  me at the end of each afternoon bearing a plate of home-baked   23  as she waited breathlessly to hear about my   24  day at school．Mom loved her family without question, but as an elementary-school teacher she had her own exciting days to   25   .She had hardly any extra time and   26 , and home-baked treats were rare in our house except   27  very special occasions．Since Mom didn't make cookies very often, the   28  of her baking were not always the same．Sometimes the cookies were browned a little more than planned or   29  together and other times the cookies weren't smooth．  30 , none of that bothered anyone in the family．All we   31  was swallowing whatever we were having for dinner that night so we could get to the cookies   32  us on the kitchen counter．Now that I'm a mom myself, I can   33  all too well why my mother didn't always have the time to wear the apron．As was true with my mother, the list of things I need to do is often   34 than the day itself．But I also understand the desire to   35  the same yellow mixing bowl my mother used and make something special for my family every so often．Whatever I bake is met with approval, appreciation and good   36  by my husband and children．At some level, I believe they're   37  that I was thinking about them as I   38  the brown sugar into the butter or frosted the cake with their favorite kind of icing．They always know I love them．I  39  they know it a little better when I'm in a baking mood．I'm sure my mother felt   40  the same way whenever she made cookies for us．Those cookies will always, in my mind, be the best treat．小题1:A．wearingB．holdingC．takingD．throwing小题2:A．watchB．greetC．guideD．encourage小题3:A．vitaminsB．vegetablesC．cookiesD．fruits小题4:A．boring B．frighteningC．comfortableD．exciting小题5:A．start withB．set upC．make upD．deal with小题6:A．powerB．workC．energyD．strength小题7:A．on B．atC．inD．by小题8:A．methodsB．resultsC．effortsD．ways小题9:A．putB．piledC．stuckD．tied小题10:A．BesidesB．HoweverC．MeanwhileD．Thus小题11:A．gave upB．cared aboutC．figured outD．cut down小题12:A．waiting forB．looking forC．longing forD．heading for小题13:A．predictB．admitC．commentD．understand小题14:A．longerB．heavierC．higherD．tighter小题15:A．put awayB．take onC．get outD．come about小题16:A．appetitesB．motivationsC．opportunitiesD．instructions小题17:A．anxiousB．awareC．eagerD．crazy小题18:A．shookB．removedC．toreD．mixed小题19:A．stateB．stressC．imagineD．complain小题20:A．mostlyB．possiblyC．reallyD．exactly