Teachers are some of the most important professionals in the wor

Teachers are some of the most important professionals in the world. They are responsible_____（21）preparing future generations to become productive and honest citizens, who will_____（22）to society for the whole of their adult life.
Obviously, the most common reason_____（23）teachers decide to teach is the ability to make a difference. There are many professions that give people the ability to have a(n) _____（24）impact on the world and change people's lives, _____（25）few professions have a direct impact on_____（26）a better society as teachers do. People tend to_____（27）their teachers for years after they finish school, for good teachers can_____（28）their students to become something that they_____（29）thought they could be, or to work_____（30）a field that they thought they did not_____（31）.
Teachers are also important because they provide_____（32）for their students. In certain low-income areas_____（33）some students may not have both of their parents _____（34）, teachers can provide an important influence that helps their students make the right_____（35）, even when they are not in the classroom. Generally, teachers' impact on students can last all through their life.
30._____
A、in
B、on
C、as
D、at
【正确答案】：A
【题目解析】：介词辨析题。本句句意：好的老师可以激励他们的学生成为他们从未想过成为的样子，或者在他们认为无法胜任的领域工作。in a field意为“在某一领域”，符合题意，故选A。