诵读下列例句并感知画线部分的共性
1．(教材P62)There are many reasons why this has been possible, but one of the main factors has been the Chinese writing system.
2．(教材P62)Emperor Qinshihuang united the seven major states into one unified country where Chinese writing system began to develop in one direction.
3．(教材P64)I told my mum that I wanted to give up, and that I would never live in a country where German was spoken.
4．(教材P64)I finally understood the reason why my mum had encouraged me not to give up.
5．(教材P68)Then I saw an advertisement that offered a wonderful summer course, and that was the day when I decided to take on a new language.
6．The time when I first met Nelson Mandela was a very difficult period of my life.
