Bitwise Blend ~ Multiplex Coder

Chef loves bitwise operations. So, he creates the following problem but needs your help to solve it.

Chef calls a sequence of integers $A_{1}, A_{2}, \dots, A_{N}$ tasty if it satisfies the following condition:

$p a r i t y (A_{i} & A_{i + 1}) \neq p a r i t y (A_{i} | A_{i + 1})$ for $1 \leq i < N$ .

Chef gives you a sequence $A_{1}, A_{2}, \dots, A_{N}$ . You may perform the following operation on the sequence any number of times (possibly $0$ ):

Choose $2$ indices $i$ and $j$ ( $1 \leq i, j \leq n$ ; $i \neq j$ ) and change $A_{i}$ to $A_{i} \oplus A_{j}$ .

Chef is asking you to make the sequence tasty using the minimum number of operations, or report that it is impossible.

As a friendly reminder,

The first line of the input contains a single integer $T$ denoting the number of test cases. The description of $T$ test cases follows.
The first line of each test case contains a single integer $N$ .
The second line contains $N$ space-separated integers $A_{1}, A_{2}, \dots, A_{N}$ .

For each test case:

If it is impossible to convert the given sequence into a tasty sequence using the given operations, print a single line containing the integer $- 1$ .
Otherwise, first, print a line containing a single integer $M$ ― the minimum number of operations you have to perform.
Then, print $M$ lines describing these operations in the order in which you want to perform them. For each $k$ ( $1 \leq k \leq M$ ), the $k$ -th of these lines should contain two space-separated integers $i$ and $j$ ( $1 \leq i, j \leq n$ ; $i \neq j$ ) ― the indices on which the $k$ -th operation is performed.

If there are multiple solutions, you may find any one of them.

Subtask #1 (100 points): Original constraints

-1
1
1 3

Test case $1$ : It is impossible to make $A$ tasty using the given operations.

Test case $2$ : We can choose $i = 1$ and $j = 3$ and apply the operation which converts $A$ into $[67, 16, 69]$ which is tasty.