1.Andrea Posasenti was able to double his money by investing in the website design company.

전치사 by뒤라서 -ing형태가 오는건가요? 잘 이해가 안가요

2.Ms. Sanders said that the transportation strike is mostly what accounts for the heavy traffic congestion.

여기에서 what이하 부분이 명사절인가요?

3.Reserved seating to the concert is available at the box office for additional fee.

왜 seat이 아닌 seating인지 설명해 주세요

4.only those with boarding passes are permitted in the departure lounge.

여기에서 that인지 this인지 근거를 어디서 찾을 수 있어서 that의 복수 those가 오는건지 모르겠어요

5.Despite having received additional suppliers for the building site, the construction was still behind schedule.

무슨 용법인지조차 모르겠어요 해석까지 상세하게 설명해주세요

6.Because of exceptional planning, the engineering firm completed the office tower earlier than expected.

왜 명사 plan이 아닌 planning이 오는건가요?