You can add a negative bottom margin to your elements then hide the overflow. This will hide the unwanted borders.
.qa {
border-bottom: 1px solid #ccc;
margin-bottom:-1px;
margin-top:1px; /*to rectify the bottom margin, we can also consider padding-bottom*/
/*irrelevant styles*/
padding: 5px;
margin-left:5px;
margin-right:5px;
box-sizing: border-box;
flex:1 1 40%;
}
.wrapper {
display: flex;
flex-wrap: wrap;
flex-direction: row;
overflow:hidden;
}
<div class="wrapper">
<div class="qa">
<div>Question</div>
<div>Answer<br>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer<br>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer</div>
</div>
<div class="qa">
<div>Question</div>
<div>Answer<br>Answer</div>
</div>
</div>
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