Solution:

The volume of the large solid object is $3\cdot 3\cdot 2 = 18$ and volume of the smaller object is $2\cdot 2\cdot 1=4.$ This means we can fit at most $4$ of the small objects.

We can make this happen by putting $3$ of the small objects in a $3 \times 2 \times 2$ rectangular prism, and then we have a $3 \times 2 \times 1$ space left where we can place one small object.

Thus, the correct answer is B .