  We recently reported [1,2] measurements of the charge density fluctuations in
the strange metal cuprate Bi$_{2.1}$Sr$_{1.9}$Ca$_{1.0}$Cu$_{2.0}$O$_{8+x}$
using both reflection M-EELS and transmission EELS with $\leq$10 meV energy
resolution. We observed the well-known 1 eV plasmon in this material for
momentum $q\lesssim$ 0.12 r.l.u., but found that it does not persist to large
$q$. For $q\gtrsim0.12$ r.l.u., we observe a frequency-independent continuum,
similar to that observed in early Raman scattering experiments [3,4], that
correlates highly with the strange metal phase [2].
  In his Comment (arXiv:2103.10268), Joerg Fink claims we do not see the
plasmon, and that our results are inconsistent with optics, RIXS, and the
author's own transmission EELS measurements with $\sim$100 meV resolution from
the early 1990's [5,6]. The author claims we have made a trigonometry error and
are measuring a larger momentum than we think. The author asserts that the
two-particle excitations of cuprate strange metals are accurately described by
weakly interacting band theory in RPA with corrections for conduction band
carrier lifetimes and Umklapp effects.
  Here, we show that the author's Comment is in contradiction with known
information from the literature. At $q\lesssim0.12$ r.l.u. we see the same 1 eV
plasmon as other techniques. Moreover we compute our momentum correctly,
adjusting the sample and detector angles during an energy scan to keep $q$
fixed. The only discrepancy is between our data and the results of Ref. [5] for
$q\gtrsim0.12$ r.l.u. where, because of the coarse resolution used, the data
had to be corrected for interference from the elastic line. A reexamination of
these corrections in early transmission EELS measurements would likely shed
light on this discrepancy.
