In president kennedy's 1963 civil rights address, the phrase "heart of the question" most likely means what?

What rule applies most closely to this word? predict- group i. if the root is a full word, the ending is usually -able. group ii. when the root is a full word except for a final e, the forms usually are spelled with -able. group iii. the suffix -able always follows i. group iv. when the root has other forms built on the letter a, the -able form is used. group v. when the root ends in hard c or hard g, -able is used. group vi. when the root is not a full word,-ible is used. group vii. when the word has an immediate -tion form, -ible is used. group viii. when the root ends in ns, miss, or soft c or g, ible is used.