Hey All,

I'll weigh in, though there's already been some good conversation:

Most space missions that seek to map cosmological expansion involve studying red-shift induced changes in the spectral content of supernovae, but a number of recent proposals would suggest tracing baryon acoustic oscillations as indicators of age.

A would suggest tracing
B are offering the suggestion of tracing
C trace
D offer the tracing
E offer the alternative of tracing

(A) "Would" implies that this is conditional, rather than definitive. The meaning here, however, is that the proposals already exist, and so the proposals simply "suggest tracing" (which would be my favorite answer, if it were here).
(B) Redundant to "offer the suggestion". Why not just suggest?
(C) "Trace" would simply modify proposals. But a proposal can't actually do this...the mission itself would do it.
(D) The proposals don't "offer the tracing". I'm not even sure what that would mean. How can you offer the tracing? That's like saying: "I offer you the massaging of your back."
(E) Correct. "Of tracing" modifies "alternative," describing exactly what kind of alternative it is. Perfecto.

Hope that helps!

-t