"By the end of" is a prepositional phrase that is often used to denote an action or state that occurs or is completed before the end of a certain point in time. When "by the end of" is used to lead a clause, it is often used in conjunction with the perfect tense to emphasize the action or state that has been completed before a specific point in time.
The specific voice used depends on the tense and context of the main clause. Here are a few common usages:
Present perfect tense: When the main clause uses the present tense, the clause usually uses the present perfect tense to denote the action or state that has been completed so far.
Example: By the end of this year, I h**e completed all my studies(By the end of the year, I had completed all of my studies.) )
Past Perfect Tense: When the main clause uses the past tense, the clause usually uses the past perfect tense to denote an action or state that has been completed before a certain point in the past.
Example: By the end of last month, they had sold all their products(By the end of last month, they had sold out of all their products.) )
Future Perfect Tense: When the main clause uses the future tense, the clause usually uses the future perfect tense to denote the action or state that is expected to be completed by some point in the future.
Example: By the end of next week, we will h**e finished the project(By the end of next week, we'll be done with the project.) )
It is important to note that "by the end of" is usually followed by a time noun or phrase, not a clause. If "by the end of" is followed by a clause, then the clause is usually a temporal adverbial clause that describes a specific point in time or time period.
For example: by the end of the time when he finished his studies, he had decided to become a teacher(By the time he finished his studies, he had decided that he wanted to become a teacher.) In this example, "the time when he finished his studies" is an adverbial clause that describes the specific point in time when "he finished his studies".