I'm serious__learning English.该填哪个介词

I'm serious__learning English.该填哪个介词 填介词 I'm ____America English 填介词 填哪个介词？ I must work hard ___a student 填哪个介词? I am very happy() that thing 填哪个介词 good luck____you_____your english填介词 I'm ( 此处填介词) dute today They are hands ( ) English里的括号里填哪个介词 I like English,I want to make friends( )some American 填介词 I could pass in English exam.I am sure 填介词 that. i could pass in English exam . i sure （ ）that. 括号内填介词