Critical Reasoning

Mr. Arlekino: Burat Company, which ordered a large lot of bolts from our company, requested that we use SP23 to manufacture those bolts, because SP23 is more efficient and produces bolts of higher quality than most of the other bolt-producing machines. Our only SP23 is currently broken and will not be fixed for three days, and the deadline for completing the order cannot be moved. Therefore, we will be forced to disregard Burat's request and use our SP20 machine, which is less efficient but is in working condition, allowing us to meet the deadline.

The argument above assumes which of the following?
(A)No other bolt producing machine is more effective and produces bolts of higher quality than SP23.
(B)By the time SP23 is repaired, SP20 will have completed the order.
(C)The quality of bolts produced by SP20 is higher than the quality of bolts produced by SP23.
(D)For any currently available bolt-producing machine other than SP20, it would be impossible to complete the order on time.
(E)Time saved during production of bolts by the more efficient SP23 would not be sufficient to compensate for the three days lost to its repair.

IMO, option E. The correct assumption must be true for the conclusion to remain intact.
If we negate E, we get "Time saved by SP23 WILL BE enough to compensate the 3 days of repair". If that is true, it means that SP20 would take 6 days for production whereas SP23 would take only 3 days so we can wait for SP23 to be repaired instead of using SP20. This makes the conclusion fall apart.
If we negate B, we get "By the time SP23 is repaired, SP20 will NOT have completed the order". So SP23 could be used to produce the remaining bolts but still SP20 would have to be used.The conclusion would not fall apart.
If we negate D, we get that another machine can produce the bolts on time. But it's possible that SP20 produces bolts of higher quality than the other machine. So the conclusion doesn't fall apart.
Option C is clearly not true.