Bonjour Kay,

1. un effet = an effect    -   an effort = an effort

2. 'Sembler' is as good an option as 'paraître' in this sentence. The phrase 'best answer' is used because it might be the one sentence/vocabulary item that comes first to mind or is the one predominantly used. But it isn't always as clear cut as this and therefore we use the other phrases 'you could also say / or also' to indicate that there are other options (which are as valid as the 'best answer'). 

I hope this is helpful.

Bonne journée !