Related Clues:

• Not even so-so grades
• Poor passable marks
• Barely-passing grades
• Poor report card
• Divided trio?
• Start of D-Day?
• Shoddy pair?
• Diamond brackets?
• Diamond Head's surroundings
• Addition takes two
• Old-fashioned endings?
• Low passing grades
• Defend borders?
• Edges of a diamond?
• Letters after cees