A、Sell pens. B、Repair pens. C、Develop pens. D、Making pens. A原文提到Parker 的sideline，这个单词是“兼职”的含义，他的兼职是钢笔公司的agent (代理)，因此可知他兼职卖钢笔。文

Since man first scrawled in the dirt with his finger, people have searched for better ways to record the written word. Today, that quest is perhaps best exemplified by one of the writing instrument industry’s leaders: Parker Pen.
    In America, the pen-making industry officially began in 1809. But, it wasn’t until the 1880s that the fountain pen as we now know got its start. Among the early industry leaders was George Safford Parker, a school teacher from Janesville, who became frustrated with the unreliability of the writing instruments then available to his students.
    To improve his insufficient teaching salary, Parker had a sideline as an agent for John Holland fountain pens. The pens were unreliable, delivering too much ink at times and at other times, no ink at all. In any case, Parker felt obligated to repair the pens he sold to his students. So, he purchased a few small tools, and began to learn the inner workings of fountain pens. As the students learned they could depend on their teacher to keep their pens in working order, the number of pens he sold increased, so did his frustration. Finally, he decided he could make a better pen himself. And he did.
    Parker patented his first fountain pen design on December 10, 1889. Two years later he entered a partnership with insurance man W. E Palmer and in February of 1892 they incorporated the Parker Pen Company.