Answer:
B. use light of a shorter wavelength.
Explanation:
We know that

h= plank's constant
c= speed of light
λ= wavelength of the incident light
so, in order to have sufficient energy for for the emission of electron, the incident's radiation must have λ small enough.
B. use light of a shorter wavelength.
If the probes are identical, then the one that feels a larger gravitational
force is orbiting closer to Jupiter than the other one is.
If they're not identical, then the one with greater mass will feel more
gravitational force than the one with less mass, even if they're both
the same distance from Jupiter. (We know this from the experimental
observation that fatter people weigh more, even on Earth.)
C. during the same time span and from the same material as the sun