a) I am a secretary for for five years.
i) Simple present instead of the present perfect
ii) First language transference
iii) The speaker has five years of experience as a secretary. This started in the past and continues until now. To express this, we use have + past participle. This form is called the "present perfect". Here is the correct sentence: I have been a secretary for five years. This means that the speaker became a secretary five years ago and is still a secretary now. Once again, in order to express this, it is necessary to use the present perfect, not the simple present. The simple present just speaks of what is true now. It does speak in an explicit way about the past, as the present perfect does.