#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

#define rd_init() char*rp=({char*mmap();mmap(0l,1l<<25,1,2,0,0ll);})
#define rd() ({int _v=0,_c;while(_c=*rp++-48,_c>=0)_v=_v*10+_c;_v;})
#define WTHI(v) {unsigned _z=v,_n=0;long _d=0;while(++_n,_d=_d<<8|0x30|_z%10,_z/=10);*(long*)wp=_d;wp+=_n;}
#define wt(v) if(v>=100000000){WTHI(v/10);*wp++=v%10+'0';}else{WTHI(v);}
#define rep(v,e) for(typeof(e)v=0;v<e;++v)
#define times(e) for(typeof(e)_=e;_--;)
#define MD 998244353

typedef unsigned long ulong;

char wbuf[1<<25];

long modpow(long a, ulong b){
	long r=1;
	while(b){
		if(b&1){
			r=r*a%MD;
		}
		b>>=1;
		a=a*a%MD;
	}
	return r;
}

int main(){
	char*wp=wbuf;
	rd_init();
	int t=rd();
	times(t){
		int n=rd();
		int k=rd();
		ulong z=1;
		ulong y=1;
		rep(i,n){
			y=y*k%MD;
			z=z*(y-1)%MD;
		}
		ulong b=0;
		rep(i,n){
			ulong a=rd();
			b+=(i+1)*(a-1);
			b-=b>=(ulong)(MD-1)*(MD-1)?(ulong)(MD-1)*(MD-1):0;
		}
		ulong c=k;
		while(b){
			if(b&1){
				z=z*c%MD;
			}
			b>>=1;
			c=c*c%MD;
		}
		wt(z);
		*wp++='\n';
	}
	write(1,wbuf,wp-wbuf);
	_exit(0);
}