Solution: From the square sum theorem of diagonal lines on four sides of parallelogram, we can get:

2AB？ +2AD？ =AC？ +BD？

2*2? +2*3? =4? +BD？ , BD = √ 10, choose B.

The sum of squares theorem of four diagonal lines of parallelogram: the sum of squares of four sides of parallelogram is equal to the sum of squares of diagonal lines. That is, if the sides of a parallelogram are A and B and the diagonal is C and D, then 2a? +2b？ =c？ +d？