Answer:
b. E-mail facilitates collaboration between people in remote locations; however, when collaboration requires the exchange of large data files, it is often easier to use web-based collaboration software.
d. E-mail can be an efficient way to communicate, and it makes communicating across time zones much easier.
Step-by-step explanation
Sentence B is correct because it employs the use of a semicolon to separate two independent clauses. The use of the conjunction, however, helps to separate two sentences that have opposite connotations.
Sentence D is correct because the conjunction, and, was used appropriately to add a second thought to the sentence. The comma was also used correctly as it spliced the sentence and was immediately followed by the conjunction, and.