The [that] in this sentence actually acts as a relative pronoun, with its antecedent being [students] instead of [jobs], which will come obvious as you omit the other relative clause led by [who].
2008-01-19 16:25:51 補充：
In other words, there are two relative clauses in this sentence, and it is the one which is led by [that] that constitutes the later half of a so called "cleft sentence."
2008-01-20 11:12:01 補充：
2008-01-20 11:12:16 補充：
再簡化: IT IS students THAT succceed in the long run.
是的, 在這句中, [that]就是關代, 先行詞是[student].
[WHO/THAT show motivation and enthusiasm towards their jobs]
2008-01-20 11:12:49 補充：
IT IS those students WHO/THAT show motivation and enthusiasm towards their jobs THAT/WHO succeed in the long run.
2008-01-20 11:13:05 補充：
You got it!
IT IS those students [WHO show motivation and enthusiasm towards their jobs(關係子句1, 修飾student) [THAT succeed in the long run(關係子句2, 一樣是修飾student, 並構成分裂句)].
2008-01-20 11:13:24 補充：
從您的回答中看得出您對文法方面是一位高手, 也有令人佩服的熱忱. 有意見大家提出討論是好事啊. ^_^