He was so slow that many thought him mentally retarded.

他迟钝得很,许多人以为他智力低下。

The heavy rain retarded our progress.

大雨妨碍了我们进展。

The problem of validity when tests are used in minority groups or for the educationally-mentally retarded.

Ⅱ、正确处理少数区及弱智童测试工作中测验效度问题。