[求助]请教OG 12 67

Affording strategic proximity to the Strait of Gibraltar,Morocco

 was also of interest to the French throughout  the first half of

the twentieth century because they assumed that if they did

not hold it, their grip on Algeria was always insecure.

(A)  if they did not hold it ,their grip on Algiria was always insecure

(B)  without it their grip on Algiria would never be secure

(C)  their grip on Algiria was not ever secure if they did not hold it

(D)  without that,they could never be secure about their grip on Algiria

(E)  never would their grip on Algiria be secure if they did not hold it

我搞不清这题的代词，题目中第一个they和it分别指的是什么?

谢谢，我明白了~

而且了解了A was also of interest to B是B对A有兴趣，一开始怎么也不明白貌似是主语的Morocco怎么就用they指代了。