[填空题]
What are the wavelengths of x:w.c8bf+y)6flxa tc the two photons prod g/t)c0)wqn1ownzkf2.,3vnqvn orex-ac/j, uced when a proton and antiproton at rest annihilatv/g, toc. ,zwcq)n/n fo-2arvnx we3j)nq1k0e? $2m_0c^2$$\approx $ $ \times 10^{-15}\ \text{m}$
