7. 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 Algeria was always insecure

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

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

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

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

正确为B. 这句话中的代词有点不太清楚， they和their是指什么？ 还有就是it又是指什么？