有三个关系R、S和T如下：则由关系R和S得到关系T的操作是 A．自然连接 B．交 C

     I used to hate being called upon in class mainly because I didn't like attention drawn to myself. And
__1__ otherwise assigned (指定) a seat by the teacher, I always __2__ to sit at the back of the
classroom.
     All this __3__ after I joined a sports team. It began when a teacher suggested I try out for the
basketball team. At first I thought it was a crazy __4__ because I didn't have a good sense of balance,
nor did I have the __5__ to keep pace with the others on the team and they would tease me. But for the
teacher who kept insisting on my "__6__ for it", I wouldn't have decided to give it a try.
     Getting up the courage to go to the tryouts was only the __7__ of it! When I first started __8__ the
practice sessions, I didn't even know the rules of the game, much __9__ what I was doing. Sometimes
I'd get __10__ and take a shot at the wrong direction-which made me feel really stupid.__11__, I wasn't
the only one "new" at the game, so I decided to __12__ on learning the game, do my best at each
practice session, and not be too hard on myself for the things I didn't __13__"just yet".
     I practiced and practiced. Soon I knew the __14__ and the "moves". Being part of a team was fun
and motivating. Very soon the competitive __15__ in me was winning over my lack of confidence. With
time, I learned how to play and made friends in the __16__-friends who respected my efforts to work
hard and be a team player. I never had so much fun!
     With my __17__ selfconfidence comes more praise from teachers and classmates. I have gone from
"__18__ " in the back of the classroom and not wanting to call attention to myself, __19__ raising my
hand-even when I sometimes wasn't 100 percent __20__ I had the right answer. Now I have more
selfconfidence in myself.