"Which of the following is the strongest argument in favor of the constitutionality of free distribution of textbooks to the students at Stone School?
The purpose and effect of the free distribution of these textbooks is secular and does not entangle church and state.
The free exercise clause requires identical treatment by the state of students in public and private school
Private religious schools, like public nonsectarian schools, fulfill an important educational function. 
Religious instruction in private schools is not constitutionally objectionable.