How to use row correctly?

Question

css

1 Option :

<div class="row">
<div class="col-md-7"><input type="text" placeholder="Как вас зовут?"></div>
<div class="col-md-5"><input type="text" placeholder="E-mail"></div>                              
</div>
<div class="row">
<div class="col-md-12"><button>Отправить</button></div>
</div>

Option 2

<div class="row">
<div class="col-md-7"><input type="text" placeholder="Как вас зовут?"></div>
<div class="col-md-5"><input type="text" placeholder="E-mail"></div>
<div class="col-md-12"><button>Отправить</button></div>
</div>

Which option is correct? I'm leaning towards the first.

Answer 1

The first option, in one .row 12 col (or 24 if the grid is like this)

Answer 2

The first option is more correct, but the second one will do. Row is like a row of columns, and in theory there should be only one row of columns in one row, however, in practice this is not so important.

Answer 3

The second one is even better because after some time returning to the project or connecting a third-party person to it, it will be easier to navigate the layout without wasting time understanding where which row is.

Answer 4

All this garbage, 2 options deserve attention, these two options are good in their own way. Everything depends on the situation.
igas.com.ua/brands here is an example, you can play around with stretching.

<div class="row">
                <div class="col-xs-6 col-sm-3 col-md-2 col-lg-2">
            <a href="http://igas.com.ua/brands/6" title="AllEnergo, Олэнерго" class="thumbnail"> 
                <img src="http://igas.com.ua/img/brands/allenergo.png" style="width:160px;" alt="AllEnergo">
            </a>
        </div>
                <div class="col-xs-6 col-sm-3 col-md-2 col-lg-2">
            <a href="http://igas.com.ua/brands/22" title="Amic, Amic Energy" class="thumbnail"> 
                <img src="http://igas.com.ua/img/brands/amic.png" style="width:160px;" alt="Amic">
            </a>
        </div>
                <div class="col-xs-6 col-sm-3 col-md-2 col-lg-2">
            <a href="http://igas.com.ua/brands/16" title="ANP, Альфа-Нафта" class="thumbnail"> 
                <img src="http://igas.com.ua/img/brands/anp.png" style="width:160px;" alt="ANP">
            </a>
        </div>
...

PS: but in this situation it is more logical to use the first option.