If gcd(a,b)=d>1\gcd(a,b) = d > 1gcd(a,b)=d>1, which of the following statements are NECESSARILY TRUE?
a≡0(modd)a \equiv 0 \pmod{d}a≡0(modd)
b≡0(modd)b \equiv 0 \pmod{d}b≡0(modd)
ab≡0(modd2)ab \equiv 0 \pmod{d^2}ab≡0(modd2)
gcd(d,ab)=d2\gcd(d, ab) = d^2gcd(d,ab)=d2