Why Is the Use of Drug-Sniffing Dogs Within the Boundaries

Why is the use of drug-sniffing dogs within the boundaries of the curtilage of a house considered a violation of constitutional rights?

A) Because it is considered trespass into a constitutionally protected area
B) Because it is considered trespass into a secretive area
C) Because it is considered a violation of the First Amendment
D) Because it is considered a violation of an individual's right to own a home