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Dear student,
Please find below the answer:

The correct option is (1) i.e. both statements are correct. 

Statement A: The phylum, Chordata, is characterized by the presence of a notochord.  In sub-phylum Vertebrata, the notochord present in embryos gets replaced by a cartilaginous or bony vertebral column in adults. Thus in chordates notochord is present in the embryonic stage and may be present in some at only larval stage or throughout their life or maybe replaced by vertebral column as in vertebrates. Thus, it can be said that all vertebrates are chordates as they possess notochord in the embryonic stage but all chordates are not vertebrates as some of them do not possess vertebral columns.

Statement B: The homeotherms are warm-blooded animals. Their body temperature remains constant irrespective of changes in environmental temperature. All mammals fall in this category. Besides mammals, birds are also homeotherms. So, we can say all mammals are homeotherms but all homeotherms (like birds) are not mammals. 

Hope this information clears your doubt.

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Both statements are correct
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