`@` `\ttcolor{#CC0066}{a}``\ttcolor{#FF0066}{K}``\ttcolor{#990066}{i}`.

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`1`. My friend often goes to school on foot.

`-` walk = on foot 

`2`. My classmate goes to school by bike.

`-` Thì HTĐ: S + V-s/es/inf + O 

`3`. How much does this textbook cost ?

`-` How much + do/does + S + cost ? 

`4`. What about we studying in the library for a while ? 

`-` What about + V-ing ?

`5`. Does your class have thirty students ? 

`-` Thì HTĐ: Do/Does + S + Vo ?

`6`. Ms. Lan teaches us English.

`-` Thì HTĐ: S + V-s/es/inf + O

`7`. Their favourite activity is playing soccer after school.

`-` enjoy + V-ing 

`8`. There is a big playground in my school.

`-` There is + a/an/one/the 

`9`. The principal always says hello to the students in the morning.

`-` Thì HTĐ: S + V-s/es/inf + O