Correct the sentence below:
navigators have known for thousands of years that the ocean has variable currents, but it is only in the last half century that a reasonably clear picture has emerged of the patterns and causes of ocean currents.

(a) a reasonably clear picture has emerged of the patterns and causes of ocean currents
(b) a reasonably clear picture of the patterns of ocean currents and their causes have emerged
(c) a reasonably clear picture emerged of ocean currents, their patterns and the causes of them
(d) there have emerged a reasonably clear picture of the patterns of ocean currents and what caused them
(e) there had emerged a reasonably clear picture of the patterns of ocean currents and their causes

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.  

it can be many reasons such as they could want they're family to live and explore more two. might just want to be nice.

3.some say for the greater good or future.

4. they might want to have they're baby,kid,family explore more. people just sacrifice.

true fact:

someone is sacrificed everyday.

tree and the cat in the tree