1 has been 

-> thì HTHT có chữ since nhận bt 

-> s + have / has + VPII + since + 1 mốc thời gian 

2 go 

-> thì HTĐ 

-> sometimes là dấu hịu nhận bt của thì HTĐ 

-> they + v nguyên mẫu 

3 have - studied

-> thì HTHT 

-> how long + have / has + S + VPII 

4 saw

-> thì QKĐ 

-> có chữ last sunday nhận bt 

5 haven't met

-> thì HTHT có chữ since nhận bt 

-> s + have / has + VPII + since + 1 mốc thời gian 

-> sau since + thì QKĐ 

6  are playing 

-> thì HTTD 

-> s +be + V-ing 

-> có chữ now nhận bt

1.Mary had been seriously ill since last night ( HTHT )

2.They sometimes go school by bus ( HTĐ ) chủ ngữ số nhiều động từ giữ nguyên

3.How long have  you studied English ? ( HTHT) 

- l studied it for 7 years.

4.We last saw them last Sunday.( QKĐ ) 

5.l haven't met him since he moved to Hanoi.( HTHT) 

6.Now they are playing happily in the school yard( có dấu hiệu là now => HTTD )