Объясните написание последней запятой в предложении:
«Ещё не спустились на землю сумерки, а в небе уже одна за другой незаметно появляются бледные звёзды, ещё не успевшие разгореться.»

            2. Сколько секунд в одной минуте?

            3. Есть две широко используемые системы измерения: Метрическая система и   Английская система.

Put the verbs in brackets into the correct past tense.

1) Yuri ..... (work) on his computer for two hours before it .... (break down).

2) I ..... (mop) the floor while my brother was cutting the grass.

3) ..... (you/sleep) when the earthquake ..... (start)?

4) This time last week, I ..... (fly) to Paris.

5) Sam was really happy because he ..... (pass) all his exams.

6) Sarah ..... (clean) the house by the time  her barents ..... (come) back.

7) James ..... (wait) for a while and then ..... (open) the door to see who ..... (make) that strange noise.

8) Marion ..... (not/go) shopping because she ..... (spend) the morning with her little brother that day.