10. In the expression 1
2
3
4 each $\square$ is to be replaced by either + or $\times$. What is the largest value of all the expressions that can be obtained in this way?

A 10
B 14
C 15
D 24
E 25
10. E If $m$ and $n$ are positive integers, then $m n>m+n$ unless at least one of $m$ or $n$ is equal to 1 , or $m=n=2$. So, to maximise the expression, we need to place multiplication signs between 2 and 3 and between 3 and 4 . However, we need to place an addition sign between 1 and 2 because $1+2 \times 3 \times 4=25$, whereas $1 \times 2 \times 3 \times 4=24$.