#include<bits/stdc++.h>

#define ll long long
#define pi pair<int,int>
#define vi vector<int>
#define cpy(x,y,s) memcpy(x,y,sizeof(x[0])*(s))
#define mset(x,v,s) memset(x,v,sizeof(x[0])*(s))
#define all(x) begin(x),end(x)
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define ary array
#define IL inline
#define eb emplace_back
#define For(i,j,k) for(int i=(j);i<=(k);i++)
#define Fol(i,k,j) for(int i=(k);i>=(j);i--)

#define mod 1000000007
#define N 1502
#define B 501
#define M 101

using namespace std;
int read(){
    int x=0,f=1;char ch=getchar();
    while(ch<'0' || ch>'9')f=(ch=='-'?-1:f),ch=getchar();
    while(ch>='0' && ch<='9')x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
    return x*f;
}
void write(int x){
    if(x<0)x=-x,putchar('-');
    if(x/10)write(x/10);
    putchar(x%10+'0');
}

void debug(auto &&...x){
    ((cerr<<x<<' '),...);
    cerr<<'\n';
}

IL int pls(int x,int y){return (x+y>=mod?x+y-mod:x+y);}
IL int sub(int x,int y){return (x-y<0?x-y+mod:x-y);}
IL void Add(int &x,int y){x=pls(x,y);}
IL void Dec(int &x,int y){x=sub(x,y);}
IL int mul(int x,int y){return x*1ll*y%mod;}
IL int qp(int x,int y=mod-2){int ans=1;while(y){if(y&1)ans=mul(ans,x);x=mul(x,x);y>>=1;}return ans;}

int fac[N*M],ifac[N*M],inv[N*M];
IL int C(int x,int y){return mul(fac[x],mul(ifac[y],ifac[x-y]));}
IL void init(){
    fac[0]=ifac[0]=inv[0]=inv[1]=1;
    for(int i=1;i<N;i++)fac[i]=mul(fac[i-1],i);
    ifac[N-1]=qp(fac[N-1]);
    for(int i=N-2;i>=1;i--)ifac[i]=mul(ifac[i+1],i+1);
    for(int i=2;i<N;i++)inv[i]=mul((mod-mod/i),inv[mod%i]);
}

int f[N*M],g[N][N],h[N][N],coef[N],a[N];

int main(){
    #ifdef EAST_CLOUD
    freopen("a.in","r",stdin);
    //freopen("a.out","w",stdout);
    #endif

    int n=read(),m=read();init();n*=m;
    For(i,1,n)a[i]=read();
    f[0]=1;
    For(i,1,n)Fol(j,n/m,1)Add(f[j],mul(f[j-1],a[i]));
    g[0][0]=1;
    For(i,0,n/m){
        For(j,0,n/m){
            if(!g[i][j])continue;
            For(k,1,n/m){
                if(k*m-1>=min(B,n))break;
                if((k+j)*m-(i+1)>n)break;
                Add(g[i+1][j+k],mul(g[i][j],C((j+k)*m-(i+1),j*m-i)));
            }
        }
    }

    h[0][0]=1;
    For(i,0,n/B){
        For(j,0,n/m){
            if(!h[i][j])continue;
            For(k,B/m,n/m){
                if(k*m-1<B)continue;
                if((k+j)*m-(i+1)>n)break;
                Add(h[i+1][j+k],mul(h[i][j],C((j+k)*m-(i+1),j*m-i)));
            }
        }
    }
    For(i,0,n/m){//总共多少组
        For(j,0,min(n/B,i))For(k,0,n/m){
            if(!h[j][k])continue;
            int coef1=h[j][k],coef2=g[i-j][n/m-k];
            Add(coef[i],mul(mul(coef2,coef1),mul(C(n-i,k*m-j),C(i,j))));
        }
    }
    int res=0;
    For(i,1,n/m)Add(res,mul(f[i],coef[i]));
    write(res);
    return 0;
}