In general terms, normally a cell in your body crosses a checkpoint in the cell cycle when
a. it receives a "go-ahead" signal directly from your brain
b. concentrations of proteins in the cytoplasm reach the appropriate level
c. it receives a "go-ahead" signal from your external environment
d. concentrations of dna in the nucleus reach the appropriate level
e. a mutation in the dna occurs

B. Concentrations of proteins in the cytoplasm reach the appropriate level

Explanation:

We can say that the cell cycle checkpoints is an important cell cycle control. In this regard, it is important to note that within a cell, the passage from one phase to another is controlled by regulatory factors that are characteristically proteinic and act at the so-called cell cycle checkpoints.

A cell passes the first checkpoint when protein concentrations in the cytoplasm reach the appropriate level.

the transfer of energy between two molecules spaced just nanometers apart plays a key role in many technologies, including photovoltaics, quantum information systems, lighting, and sensors, as well as in biophysics to measure nanometer distances and in photosynthesis. but an open question in this area is what effect, if any, the surrounding photonic environment has on this nanoscale energy transfer. by designing and performing a carefully controlled experiment to answer this question, scientists have settled the debate and found clues to improving the efficiency of many of the technologies that rely on this process.

explanation: