// ---------- begin scannner ----------
#[allow(dead_code)]
mod scanner {
    use std::str::FromStr;
    pub struct Scanner<'a> {
        it: std::str::SplitWhitespace<'a>,
    }
    impl<'a> Scanner<'a> {
        pub fn new(s: &'a String) -> Scanner<'a> {
            Scanner {
                it: s.split_whitespace(),
            }
        }
        pub fn next<T: FromStr>(&mut self) -> T {
            self.it.next().unwrap().parse::<T>().ok().unwrap()
        }
        pub fn next_bytes(&mut self) -> Vec<u8> {
            self.it.next().unwrap().bytes().collect()
        }
        pub fn next_chars(&mut self) -> Vec<char> {
            self.it.next().unwrap().chars().collect()
        }
        pub fn next_vec<T: FromStr>(&mut self, len: usize) -> Vec<T> {
            (0..len).map(|_| self.next()).collect()
        }
    }
}
// ---------- end scannner ----------

use std::io::Write;
use std::collections::*;

type Map<K, V> = BTreeMap<K, V>;
type Set<T> = BTreeSet<T>;
type Deque<T> = VecDeque<T>;

fn main() {
    use std::io::Read;
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).unwrap();
    let mut sc = scanner::Scanner::new(&s);
    let out = std::io::stdout();
    let mut out = std::io::BufWriter::new(out.lock());
    run(&mut sc, &mut out);
}

fn run<W: Write>(sc: &mut scanner::Scanner, out: &mut std::io::BufWriter<W>) {
    let t: u32 = sc.next();
    for _ in 0..t {
        let n: usize = sc.next();
        let a: Vec<usize> = sc.next_vec(n);
        if let Some(a) = solve(a.clone()) {
            writeln!(out, "{}", a.len()).ok();
            for a in a {
                writeln!(out, "{} {}", a.0 + 1, a.1).ok();
            }
        } else {
            writeln!(out, "-1").ok();
        }
    }
}

fn solve(mut a: Vec<usize>) -> Option<Vec<(usize, usize)>> {
    let mut ans = vec![];
    let n = a.len();
    while let Some(x) = (0..n).max_by_key(|x| a[*x]) {
        let v = a[x];
        if v == 0 {
            break;
        }
        ans.push((x, v));
        a[x] = 0;
        let mut c = 0;
        for a in a.iter_mut() {
            if *a ^ v < *a {
                c += 1;
                *a ^= v;
            }
        }
        if c > 1 {
            return None;
        }
    }
    Some(ans)
}