Respostas
1 - wear / were
2 - bought / would drive
3 - studied / wouldn't fail (não fala de colocar a segunda oração na negativa "not", mas claramente precisa tá na negativa senão a frase não faz sentido nenhum, e ficaria melhor a frase no third conditional, mas como a questão pede tudo no second, respondi como tal)
4 - had / would buy
5 - would be / danced
6 - drank / would drink
7 - were / wouldn't smoke (nesse trocaram a ordem das orações, era pra ser "if you didn't smoke, you would be healthier", mas trocaram os verbos)
8 - spoke / would get
9 - met / would tell
10 - weren't / would eat
11 - would you do / rained
12 - would help / could
13 - prepared / would come (esse ficaria melhor no first ou third conditionals, mas respondi no second já que a questão pede assim)
14 - wouldn't be / cacme
15 - wouldn't have / lived
16 - could speak / would get
17 - took / would arrive (esse ficaria melhor no third conditional)
18 - wouldn't stay / sang (esse também fica melhor no first ou third conditional)
19 - were / would live
20 - won / would buy
21 - drove / would give