What is the nature of physical objects according to the text?

Physical objects are completely similar to our sensory data.
Physical objects are the cause of our sensory experiences.
The nature of physical objects is unknown in itself.
The nature of physical objects can be directly perceived through our senses.
a) Only I and II are correct.
b) Only II and IV are correct.
c) Only III is correct.
d) Only II and III are correct.