A. Like other French generals of the time, General Serrail was an architect of war, and in 1916, in a move to further the control of the central powers over the Balkans, demanded that the Greek army
demobilizesB. Like other French generals of the time
were, General Serrail was an architect of war, and in 1916, in a move to further the control of the central powers over the Balkans, demanded that the Greek army demobilize
C. General Serrail was an architect of war like other French generals of the time
were, and in 1916, in a move to further the control of the central powers over the Balkans, he demanded that the Greek army demobilize
D. General Serrail, like other French generals of the time, was an architect of war, and in 1916, in a move to further the control of the central powers over the Balkans, demanded that the Greek army was
demobilizingE. General Serrail, like other French generals of the time, was an architect of war, and in 1916, in a move to further the control of the central powers over the Balkans, demanded that the Greek army
demobilizeThis post requires the use of subjunctive. With that, A and D are out since we need to use the base form of the verb demobilize.
Among B,C,E, "like" has to be used in the form of noun comparisons.
When we see "Like other French generals of the time
were" this is clearly incorrect as the noun is changed to a clause (we will have to use as) then.
Hence, E is the correct answer.