Answer:
The correct option is 1.
Explanation:
The general cosine function is

where, A is amplitude,
is period, C is phase shift and D is midline.
It is given that the Chesapeake Bay tides vary between 4 feet and 6 feet. it means the minimum value is 4 and maximum value is 6.
Amplitude of the function is



Therefore the amplitude of the function is y=5.
Midline of the function is


Therefore the midline of the function is y=5.
It completes a full cycle in 12 hours.
hours

Period of the function is 12 hours. Therefore the correct option is 1.