HTML & CSS Responsive grid with Bootstrap

[lmnu]

Hi,
I have a list of 18 items. When I am in sm I would like one column of 18 items, in md two columns of 9 items and xl three columns of 6 items.

 <div class='row'>
                            <div class='col-xl-4 col-md-6 col-sm-12'>
                                <ul>
                                    <div>Items01</div>
                                    <div>Items02</div>
                                    <div>Items03</div>
                                    <div>Items04</div>
                                    <div>Items05</div>
                                    <div>Items06</div>
                                </ul>
                            </div>
                            <div class='col-xl-4 col-md-6 col-sm-12'>
                                <ul>
                                    <div>Items07</div>
                                    <div>Items08</div>
                                    <div>Items09</div>
                                    <div>Items10</div>
                                    <div>Items11</div>
                                    <div>Items12</div>
                                </ul>
                            </div>
                            <div class='col-xl-4 col-md-6 col-sm-12'>
                                <ul>
                                    <div>Items13</div>
                                    <div>Items14</div>
                                    <div>Items15</div>
                                    <div>Items16</div>
                                    <div>Items17</div>
                                    <div>Items18</div>
                                </ul>
                            </div>
                        </div>

With "sm" and "xl" no problem but in "md" I have a first column of 12 items and the second of 6 items.
How can I have two columns with the same number of items?

Thank you for your help

 

[lmnu]

Finally I found a solution, I don't know if it is the right one but it works.
I give it for information:

<div class="container">
        <div class="d-none d-lg-block">
            <div class="row">
                <div class="col-4">Items01</div>
                <div class="col-4">Items02</div>
                <div class="col-4">Items03</div>
                <div class="col-4">Items04</div>
                <div class="col-4">Items05</div>
                <div class="col-4">Items...</div>
            </div>
        </div>
        <div class="d-none d-md-block d-lg-none">
            <div class="row">
                <div class="col-6">Items01</div>
                <div class="col-6">Items02</div>
                <div class="col-6">Items03</div>
                <div class="col-6">Items...</div>
            </div>
        </div>
        <div class="d-sm-block d-md-none d-lg-none">
            <div class="row">
                <div class="col-12">Items01</div>
                <div class="col-12">Items02</div>
                <div class="col-12">Items03</div>
                <div class="col-12">Items04</div>
                <div class="col-12">Items05</div>
                <div class="col-12">Items...</div>
            </div>
        </div>
    </div>