Final answer:
The appropriate phrase to complete the sentence is 'in that' which logically links the opinion of the proposal being good with the explanation that it saved time and money.
Step-by-step explanation:
The sentence "The proposal, in my opinion, was very good ____________. ____________...it saved time and money." is looking to be completed with a conjunction or phrase that shows a positive aspect of the proposal. The best fit from the provided options would be 'in that' which introduces a reason or explanation for the preceding statement. Therefore, the complete sentence would be: The proposal, in my opinion, was very good in that it saved time and money.
Using 'in that' here connects the fact that the proposal is good with a specific reason why it is good, which is a logical and coherent way to construct the sentence to convey a strong, positive point about the proposal.