$1$. The students have done their test since the bell rang
$2$. I haven't played badminton for a long time
`->`since + quãng thời gian
`->`for + quãng thời gian
`->`CT thì HTHT:
$+)$ S + has/have + Ved/3
$-)$ S + has/have + not + Ved/3
$?)$ Has/Have + S + Ved/3 ?