a. Even though I usually know what I have to say, I cannot always express myself correctly in English.
这句话是一个复合句，由even though引导的让步状语从句。
b. This challenges me to practice my spoken English, with the result that I can complete the speaking tasks more fluently and quickly.
这句话中是一个复合句。with介词结构中，有一个that引导的同位语从句对result进行解释说明。
c. I think this is less than ideal because any differences in opinion become personal conflicts, and therefore that might jeopardize the employee’s job.
上句话是一个并列复杂句。and 连接了两个句子，是一个并列句;because引导的原因状语从句。
d. Shallow writing is indicative of weak critical-thinking skills, and such writing, which is often described as “sophomoric”, receives low mark.
这句话同样是并列复杂句。由and连接两个句子，成为并列句，再一个which引导的定语从句。