Answer:
A). E-mail can be an efficient way to communicate, and it makes communicating across time zones much easier.
B). All e-mail, even once deleted, is retrievable and, therefore, you should avoid sending sensitive information in an e-mail.
Step-by-step explanation:
A compound sentence is elucidated as a sentence comprising of minimum of two independent clauses or more linked together in a sentence with a coordinator(coordinating conjunction, comma, or semicolon(;)) and conveys a coherent meaning together. Such sentences help in presenting thoughts coherently and avoid choppiness.
As per the questions, options A and B exemplify compound sentences appropriately as they comprise of at least two independent clauses joined together with coordinating conjunctions like 'and', 'therefore'. Option C exemplify a compound-complex sentence while option D conveys an incomplete thought.
In the first option, the two independent clauses 'E-mail can be an efficient way to communicate' and 'it makes communicating across time zones much easier'(each offers a complete thought) linked with the coordinating conjunction 'and'.
In the second options, the two clauses 'All e-mail, even once deleted, is retrievable' and 'you should avoid sending sensitive information in an e-mail' which are independent and joined with coordinating conjunctions 'and', 'therefore', etc.