医生  Mary's father is a doctor, who specialises in the field of infectious diseases. 

博士  Mary's father is a Doctor, who studied in ABC College and later graduated as a Doctor of Science. 【但是注意，表示博士的Doctor要大写首字母】

另外doctor还有各种行业类似分析师，咨询师之类的别称，不过我想中国学习用到的无非就是两种：医生和博士。后者大写首字母，所以严格说来原句没有歧义。

没放  I didn't fly the kite 【停顿】because it was a beautiful day. So I went to take photos instead. 【天气很好，不放风筝了，去拍照片了】

放了  I didn't  【停顿】fly the kite because it was a beautiful day. I flied the kite because I love flying kites.【我并非因为天气好才去放风筝的，我喜欢放风筝所以就放了】