Correct : b

To find the total time to transfer the file, we must determine the total file size in bits and identify the slowest link in the network path, known as the bottleneck bandwidth.

Calculating the Total File Size
The file size is given as 4 million bytes. Since network transmission speeds are measured in bits per second, we first need to convert bytes to bits (1 byte = 8 bits).
File Size = 4 × 10⁶ bytes = 4 × 10⁶ × 8 bits = 32 × 10⁶ bits.

Identifying the Bottleneck Bandwidth
The network path consists of three consecutive links:
Link 1: 2 Mbps = 2 × 10⁶ bps
Link 2: 500 kbps = 500 × 10³ bps = 0.5 × 10⁶ bps
Link 3: 1 Mbps = 1 × 10⁶ bps
In a multi-link network, the overall data transfer rate is always constrained by the slowest link. Comparing the three, the minimum bandwidth is 500 kbps (0.5 × 10⁶ bps).

Calculating the Transfer Time
Because network data is pipelined (sent as a continuous stream of packets) and processing/propagation delays are negligible, the total transfer time is simply the time it takes to push the entire file through that bottleneck link.
Total Time = File Size / Bottleneck Bandwidth
Total Time = (32 × 10⁶ bits) / (0.5 × 10⁶ bps)
Total Time = 32 / 0.5 = 64 seconds.

Correct Answer: B (64) ✓