A conclusion is basically rounding everything you say in your essay or writing piece at the end of the writing work
Transitions help the writer to state a broad, general idea and ease it into a more specific point that still supports that idea.
B. A possessive noun should have its instead of it's (which is a contraction for it is).
For A. Diana is a singular noun and the apostrophe should come after the r instead of after the s.
For C. The duck would've dunked ITS instead of IT'S beak since it is possessive.
For D. You do not need to put an apostrophe since theirs is already a possessive noun.