i think English is most useful of all the subjects.

问题描述:

i think English is most useful of all the subjects.

of => among

is the most useful
*前加the

i think English is most useful of all the subjects改成:
i think English is 【the】 most useful of all the subjects

希望对你有帮助
*前要加 the,表示特指
祝学习进步

English is【the】most