use std::io::Write;

fn run() {
    input! {
        t: usize,
        ask: [(usize, usize, bytes, bytes); t],
    }
    let out = std::io::stdout();
    let mut out = std::io::BufWriter::new(out.lock());
    for (n, m, a, b) in ask {
        let mut ans = vec![b'z'; n + 1];
        for i in 0..=(n - m) {
            if a[i..]
                .iter()
                .zip(b.iter())
                .all(|p| *p.0 == b'?' || *p.0 == *p.1)
            {
                let mut res = a.clone();
                res[i..(i + m)].copy_from_slice(&b);
                res.iter_mut().for_each(|c| {
                    if *c == b'?' {
                        *c = b'a'
                    }
                });
                ans = std::cmp::min(ans, res);
            }
        }
        if ans.len() == n + 1 {
            writeln!(out, "-1").ok();
        } else {
            let ans = ans.into_iter().map(|c| c as char).collect::<String>();
            writeln!(out, "{}", ans).ok();
        }
    }
}

fn main() {
    run();
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------