题目

As a disabled person, I often feel I have two jobs．There's my normal job working as a radio producer and there’s my role managing a team of carers （otherwise called personal assistants）．Of the two jobs, being a radio producer is considerably easier．One of the hardest aspects of being a PA employer and needing 24-hour care is that you never feel “off duty”．At any time a PA could present me with an issue or concern that needs handling． There was an occasion when a previous PA came into my bedroom one morning to get me up and began complaining straight away that I had paid her1. 一种人工合成的信使RNA上只含有两种核苷酸U和C，且它们的含量之比为U：C＝5：1，这种人工合成的信使RNA上，最多可构成密码子的种数为 A．4       B．61     C．64     D．8