How is stealth implemented in malware? what kinds of stealth are there?

In which phase does software coding and testing happen in the spiral model? the spiral model does not have a separate testing phase. both, software coding and testing occurs during the phase.

Consider the simple 3-station assembly line illustrated below, where the 2 machines at station 1 are parallel, i. e., the product only needs to go through one of the 2 machines before proceeding to station 2.what is the throughput time of this process?

Which cultural aspect does this type of song best portray? a german polka dance