Final answer:
Detecting planets orbiting 1% of the stars in a 3-year transit program indicates that planets are abundant in the monitored star population, acknowledging the accomplishments despite the inherent observational limitations in exoplanet detection.
Step-by-step explanation:
If your 3-year transit program detects planets orbiting about 1% of the stars you are monitoring, the conclusion (c) Planets are abundant in the observed star population could be derived. This is because, despite the challenges in detecting exoplanets due to biases such as the size of planets and their orbital periods, finding planets around 1% of the stars signifies that planets can be quite common. The Kepler mission, which focused on similar observations, dealt with these biases and still provided evidence that planets, especially those in coplanar systems with shorter orbital periods, are fairly widespread. Therefore, one should neither conclude that the program is ineffective (a) nor that the program is not observing any planets (b). Instead, the data suggests that, within the observational limitations, planets are being detected. Additionally, since the Kepler space observatory was mainly operational till 2018 and required multiple transits to confirm a planet's existence, we understand that the process is meticulous and lengthy but productive. While there might be value in extending the program (d) to detect more planets, the current detection rates already suggest that planets are not infrequent in the monitored population.