Read the given statements and conclusions carefully. Assuming that the information given in the statements is true, even if it appears to be at variance with commonly known facts, decide which of the given conclusion(s) logically follow(s) from the statements.
Statements:
I. All keys are doors.
II. Some doors are cupboards.
III. All cupboards are big.
Conclusions:
(I) Some keys are doors.
(II) All doors are cupboards.​

​Statements:
I. All keys are doors.
II. Some doors are cupboards.
III. All cupboards are big.

​Conclusions:
(I) Some keys are doors. (Follows, If all keys are doors, then definitely some keys are doors. )
(II) All doors are cupboards. (Not follow,  The statement says some doors are cupboards, not all.)

So, Only conclusion (I) follows.

Thus, correct option is (d).