Astronomy quiz question: first star to set?

Astronomy 210 Quiz 1, fall semester 2016
Cuesta College, San Luis Obispo, CA

The diagram at right shows the positions on August 30 of the constellations Leo, Cancer, and Hydra for an observer in San Luis Obispo, CA. Also shown are the stars Regulus and Alphard. Ignore daylight saving time. Assume you can see stars in daylight. Within the next 24 hours, the star __________ will eventually set first, below the horizon.
(A) Regulus.
(B) Alphard.
(C) (There is a tie.)
(D) (Neither of these stars will set below the horizon.)

Correct answer (highlight to unhide): (B)

As read off from a starwheel, Regulus and Alphard will be above the east horizon as shown at 7:00 AM on August 30. Advancing time forward (while keeping the date at August 30) indicates that while they rose at about the same time earlier that day, Alphard will set first (around 4:30 PM), while Regulus will set approximately two hours later (around 6:30 PM) that same day.

Section 70158
Exam code: quiz01swE3
(A) : 9 students
(B) : 21 students
(C) : 3 students
(D) : 10 students

Success level: 50% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.25

Section 70160
Exam code: quiz01n4Ps
(A) : 7 students
(B) : 15 students
(C) : 4 students
(D) : 5 students

Success level: 47% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.34