Поставьте частицу to перед инфинитивами после модальных глаголов, где необходимо:

I can … see;
he ought … know;
he will be able … change;
he was allowed … translate;
I may … arrive;
he could … go;
I must … do;
he has … ask;
they are … read;
they have … translate;
he should … help;
we had … build;
they may … build;
they were allowed .. answer;
he will be able … make;
he has … arrive;
she must … change;
you will be able … translate;
they should … tell;
they ought … tell the truth.