Consider these sentences, please:
1) A: Where is John?
B: He could be in the market.
2) It could be dangerous to cycle in the city.
3) Working in London next summer could be a great experience.
The three "coulds" in 1), 2) and 3) are very similar, because:
a) They look exactly the same.
b) They all mean "possibility."
c) They can all be replaced by "might."
d) They are all "tentative."
Q1) Are they completely same?
Q2) If not, how does a native speaker of English differentiate among the three "coulds", which have so much in common?