This sentence was wrong: Nowadays I am teaching science at a secondary school since 1998. “Nowadays,” sounds more informal so for a job application cover letter I would use “Currently,”
Currently, I am teaching science at a secondary school.
Alternative: At present,
[CURRENTLY is about the present, so we need a present tense, simple or continuous. The continuous tense can be used because you feel it’s a temporary situation in your life, or because you are focusing on the process.]
Since 1998 I have been teaching science at a secondary school.
Alternative: For the past 15 years
[SINCE indicates a point in the past that reaches to the present so we need a present perfect tense. The choice bt simple or continuous depends on how descriptive you want to get. In this example, the continuous form is best.]
Using the present simple: watch out!
Wrong: (in a cover job application letter) “I
study English to get the B2 level”. Here the present simple indicates a habit or a routine, and this is not the best option for this context — you do not want to talk about your routines, you want to give information about a current activity of yours, which is actually temporary. So below is a better option. Why? Can you explain?
“At the moment, I am taking an upper intermediate course (CEFR B2) to improve my English.”