The answer is B.
(A) sometimes from America and sometimes they come
This option suffers from redundancy and an incomplete phrasing at the end, disrupting the sentence's structure and coherence.
(B) sometimes from America and sometimes
This option effectively presents a clear contrast between the origins of the beef used by McDonald's. It succinctly communicates that at times, the beef originates from America, and at other times, it comes from other sources.
(C) that come sometimes from America or sometimes
The phrase "that come sometimes" doesn't fit well in the sentence structure. Additionally, the use of "or sometimes" creates ambiguity regarding the intended meaning.
(D) from America sometimes, or sometimes they come
This choice has a fragmented structure with "from America sometimes" and an awkward construction with "or sometimes they come" after the comma.
(E) from America sometimes, or sometimes coming
This option introduces awkwardness with "or sometimes coming" after the comma, disrupting the sentence's flow and coherence.