Measurements of the amount of DNA per nucleus were taken on a large number of cells from a growing fungus. The measured DNA levels ranged from 3 to 6 picograms per nucleus. In which stage of the cell cycle was the nucleus with the 6 picograms of DNA

The correct answer is G2 phase.

Explanation:

In the cell cycle, the third sub-phase of interphase that directly comes before mitosis is known as the Gap 2 phase or G2 phase. The beginning of the G2 phase takes place after the successful termination of the S phase, that is, the phase when the DNA of the cell gets replicated. Later with the beginning of prophase, that is, the starting phase of mitosis, the G2 phase culminates.  

In the G2 phase, the cell goes through brisk development and at the same time the synthesis of protein takes place, this prepares the cell for the process of mitosis. In the given question, it is clear that the cell has passed the S phase of the cell cycle as the process of DNA replication has taken place, that is, the size of DNA has increased from 3 to 6 picograms. This shows that the cell has now moved to the G2 phase of the cell cycle.  

the answer to your question is b

"do a testcross with a homozygous recessive plant."