**A, B and C**in this order (disregarding the empty cells in the string), and more, in the whole grid each letter appears in every row and in every column once, and only once.

+---+ +---+ +---+ +---+ +---+ | A |-| | | B |-| C |-| | +---+ +---+ +---+ +---+ +---+ | | +---+ +---+ +---+ +---+ +---+ | B | | A |-| | | | | C | +---+ +---+ +---+ +---+ +---+ | | | +---+ +---+ +---+ +---+ +---+ | |-| C | | | | A | | B | +---+ +---+ +---+ +---+ +---+ | | | +---+ +---+ +---+ +---+ +---+ | |-| | | C |-| B | | A | +---+ +---+ +---+ +---+ +---+ | | | +---+ +---+ +---+ +---+ +---+ | C | | B |-| A | | |-| | +---+ +---+ +---+ +---+ +---+Fill the 7 x 7 grid below the same way (there are 7 strings, each one with 7 cells), using the letters

**A, B, C and D**. One letter (D) is already placed.

+---+ +---+ +---+ +---+ +---+ +---+ +---+ | |-| |-| |-| |-| | | |-|D| +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | | | |-| | | | | | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |-| | | | | |-| | | | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | | | | | |-| | | | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |-| | | | | | | | | |-| | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | |-| |-| | | | | |-| | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |-| | | |-| |-| | | |-| | +---+ +---+ +---+ +---+ +---+ +---+ +---+