Unless they are programmed by humans, computers are nothing more than big pieces of metal. But once _____ what to do, they show extraordinary power in carrying it out.

A．taught

B．teaches

C．teaching

D．to teach

“正能量”指的是一种健康乐观、积极向上的精神动力和情感力量。下列校园生活中展现正能量的是 

①同学们服务社会，积极参与社会公益活动

②评选“先进班集体”和“校园之星”等活动

③校运会上运动健儿努力拼搏，其他同学助威呐喊

④某校毕业班的同学给母校“留下”了满地的书本和废弃物

A．①②③

B．①②④

C．①③④

D．②③④