Why are std::allocator objects being inserted into my vector? [closed]

I have two vectors of A objects. I want to "Python zip" the vectors together pairwise, go through the pairs, create a B object out of each pair, and insert each new B object into a vector. Then I need to use the vector of B objects to create a C object.

I'm trying to use std::transform to accomplish this like so:

std::vector<B> zipped;
std::transform(first_vector_of_A_objects.begin(),
    first_vector_of_A_objects.end(),
    second_vector_of_A_objects.begin(),
    zipped.begin(),
    [&](const auto& a1, const auto& a2) {
        return B::create({a1, a2});
     });
C c = C::create(zipped);

My compiler throws an error telling me that zipped is of type std::vector<B, std::allocator<B> >&) and that I need a std::vector<B> to create a C object. This doesn't make any sense! I've gone over the C++ documentation and tried several variations on the above code, and I don't see how I'm getting these std::allocator objects. Why can't I use std::transform to populate my vector with B objects?