Let's analyse this:
B. On a Snowball Edge device you can copy files with a speed of up to 100Gbps. 70TB will take around 5600 seconds, so very quickly, less than 2 hours. The downside is that it'll take between 4-6 working days to receive the device and then another 2-3 working days to send it back and for AWS to move the data onto S3 once it reaches them. Total time: 6-9 working days. Bandwidth used: 0.
C. File Gateway uses the Internet, so maximum speed will be at most 1Gbps, so it'll take a minimum of 6.5 days and you use 70TB of Internet bandwidth.
D. You can achieve speeds of up to 10Gbps with Direct Connect. Total time 15.5 hours and you will use 70TB of bandwidth. However, what's interesting is that the question does not specific what type of bandwidth? Direct Connect does not use your Internet bandwidth, as you will have a dedicate peer to peer connectivity between your on-prem and the AWS Cloud, so technically, you're not using your "public" bandwidth.
The requirements are a bit too vague but I think that B is the most appropriate answer, although D might also be correct if the bandwidth usage refers strictly to your public connectivity.