Question: appending expressions without evaluating.

Could someone help me fix this loop.

It is printing the expressions without evaluating but it is evaluating it before appending it to the list.
I do not want to apriori define the functional dependence i.e. f(t).

lis := [f1, f2, f3, f4, f5, f6, f7, f8, f9, f10];
L := [];
for i in lis do
    print(subs(f = i, 'diff(f, t)'));
    L := [op(L), subs(f = i, 'diff(f, t)')];
end do;

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