Placing no more than one $\text{X}$ in each small [square](https://artofproblemsolving.com/wiki/index.php/Square), what is the greatest number of $\text{X}$'s that can be put on the grid shown without getting three $\text{X}$'s in a row vertically, horizontally, or diagonally?
$\text{(A)}\ 2 \qquad \text{(B)}\ 3 \qquad \text{(C)}\ 4 \qquad \text{(D)}\ 5 \qquad \text{(E)}\ 6$
[asy] for(int a=0; a<4; ++a)  {   draw((a,0)--(a,3));  } for(int b=0; b<4; ++b)  {   draw((0,b)--(3,b));  } [/asy]
By the [Pigeonhole Principle](https://artofproblemsolving.com/wiki/index.php/Pigeonhole_Principle), if there are at least $7$ $\text{X}$'s, then there will be some row with $3$ $\text{X}$'s.  We can put in $6$ by leaving out the three boxes in one of the main diagonals.
$\rightarrow \boxed{\text{E}}$