Submitted on: 15 August 2000.
Revised on: 12 September 2000.
Accepted on: 07 October 2000.
Research in Developmental Disabilities
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Submitted on: 09 August 2000.
Revised on: 22 August 2000.
Accepted on: 14 September 2000.
Research in Developmental Disabilities
http://reply.papertrans.cn/3/265/26401/26401-34.png
Submitted on: 13 June 1998.
Revised on: 23 June 1998.
Accepted on: 05 July 1998.
Research in Developmental Disabilities
http://reply.papertrans.cn/3/265/26401/26401-36.png