There have been a lot of ----in our city since 1990.

答案：D
解析：当由man,woman 修饰职业名词时,变成复数时,man,woman和后面的职业名词都要变成复数,如 men teachers,women drivers等
翻译：自从1990年,我们城市已经有许多女医生了.
有不明白的请继续追问,