How Does a Regulatory Protein with a Helix-Turn-Helix Motif Recognize

How does a regulatory protein with a helix-turn-helix motif recognize a specific DNA sequence?

A) The regulatory protein opens up the two strands of DNA and detects functional groups on the bases on one of the strands.
B) The regulatory protein opens up the two strands of DNA and detects functional groups on the bases on both strands.
C) The regulatory protein detects functional groups on the base pairs that project into the major grooves of double-stranded DNA.
D) The regulatory protein detects specific sequences in the sugar-phosphate backbone of the DNA double helix.