以下哪段代码能将数组int a[4] = {2, 4, 6, 8};的所有元素变为原来的二倍?
int a[4] = {2, 4, 6, 8};
for (int i = 0; i < 4; i++) a[i] += 2;
for (int i = 0; i < 4; i++) a[i] *= 2;
for (int i = 1; i <= 4; i++) a[i] = a[i] * a[i];
for (int i = 1; i <= 4; i++) a[i] *= 2;