1. В том, что мы не ставим перед ним вс глагол don't/doesn't, а используем отрицательную форму глагола (с частицей not).
I am not a doctor [не I don't be a doctor/I don't am a doctor]
We are not doctors [не We don't be a doctor/We don't are a doctor]
He is not a doctor [не She doesn't be a doctor/She doesn't is a doctor]
2. Так же - мы не ставим вс глагол do/does на начало предложения, но ставим одну из форм глагола to be (в зависимости от лица).
Am I a doctor? [не Do I be a doctor?/Do I am a doctor?]
Are we doctors? [не Do we be doctors?/Do we are doctors?]
Is he a doctor? [не Does he be a doctor?/Does he is a doctor?]
3. always (всегда), often (часто), every day (каждый день), every year (каждый год), every week (каждую неделю), usually (обычно), sometimes (иногда), seldom (редко) (подробный список можно посмотреть в Интернете)
1) to have e) a bad headache
2) to complain m) of a sore throat
3) to suffer f) from high blood pressure
4) to take d) temperature
5) to consult l) a doctor
6) to examine c) a patient
7) to check b) eyes
8) to feel p) the pulse
9) to listen g) to the heart and lungs
10) to have the chest n) X-rayed
11) to test i) blood pressure
12) memory k) loss
13) to prescribe a) medicines
14) to have problems j) with the heart
15) to follow ? the doctor's advice
16) to take tablets h) for stomachache
17) to stay o) in bed
