Remind I’m bored if not get it

What is the answer to this question?

Of four agents alpha, beta, gamma anddelta, three have to be sent together on amission. if alpha and beta cannot gotogether, beta and gamma cannot go togetherand gamma and delta cannot go together,then which of the following holds? 1. any three agents can be sent.2. alpha, delta and any one out of beta andv gamma can be sent.3. beta, gamma and any one out of alphaand delta can be sent.4. the mission is impossible.

Remote sensing of the earth's surface and atmosphere may involve the use of what type of instruments?