  The central engine of gamma-ray bursts (GRBs) remains an open and forefront
topic in the era of multimessenger astrophysics. The X-ray plateaus appear in
some GRB afterglows, which are widely considered to originate from the spindown
of magnetars. According to the stable magnetar scenario of GRBs, an X-ray
plateau and a decay phase as $\sim t^{-2}$ should appear in X-ray afterglows.
Meanwhile, the ``normal'' X-ray afterglow is produced by the external shock
from GRB fireball. We analyze the Neil Gehrels \emph{Swift} GRB data, then find
three gold samples, which have an X-ray plateau and a decay phase as $\sim
t^{-2}$ superimposed on the jet-driven normal component. Based on these
features of the lightcurves, we argue that the magnetars should be the central
engines of these three GRBs. Future joint multimessenger observations might
further test this possibility, then which can be beneficial to constrain GRB
physics.
