经过多次尝试，他终于学会了弹吉他。

After many ___trials, he finally learned to play the guitar.

他在游泳选拔赛中表现出色，成功入选校队。

He performed well in the swimming ___trials and made the school team.

法官宣布审判将于下周一正式开始。

The judge announced that the ___trial will officially begin next Monday.

这种新药正在进行临床试验以测试其安全性。

The new drug is in clinical ___trials to test its safety.