Answer:
A
Explanation:
We eliminate B because subject is singular (picture) and does not agree with the plural verb (have emerged).
C is not correct because in the first part of the sentence we have present perfect tense (Navigators have known….), in the second part we have simple past (n the last half century that a reasonably clear picture emerged….); there is not time consistency and it is not logical.
D is also eliminated for the same reason as B.
E has ambiguity since it is not clear if the pronoun 'their' refers to patterns or to currents.
Therefore, A is the correct option.
