Fact $1:$ Humans are mammals.

Fact $2:$ Some humans are engineers.

Fact $3:$ Engineers build houses.

If the above statement are facts, which of the following can be logically inferred?

1. All mammals build houses.
2. Engineers are mammals.
3. Some humans are not engineers.
1. II only.
2. III only.
3. I, II and III.
4. I only