Concept:The underlined "th" in "think" is pronounced as the voiceless dental sound /θ/.Explanation:The word "think" is pronounced as /θ/.So the consonant sound to match is the voiceless "th" sound, not the voiced one.Now examine each option:A. "smart" has no /θ/ sound.B. "tooth" is pronounced /tu:θ/, and its final consonant is also /θ/.C. "tiny" has no /θ/ sound.D. "worthy" has the voiced /δ/ sound, which is different from the voiceless /θ/.Answer:B. tooth