CREATE TABLE table_68827 ("Date" TEXT, "Location" TEXT, "Nature of incident" TEXT, "Circumstances" TEXT, "Casualties" TEXT)

What is the nature of the incident that's a bomb attack?
SELECT "Nature of incident" FROM table_68827 WHERE "Circumstances" = 'bomb attack'
SELECT "Nature of incident" FROM "table_68827" WHERE "Circumstances" = 'bomb attack'