6. 下列图示实验中，操作规范的是
<table><tr><td><img src="https://zebfdsytobcavmuynuhx.supabase.co/storage/v1/object/public/review-images/tasks/9e598ea2-5465-454a-a28d-941fb33f7ad2/f7ab2ffc4bfbea14.jpg"/></td><td><img src="https://zebfdsytobcavmuynuhx.supabase.co/storage/v1/object/public/review-images/tasks/9e598ea2-5465-454a-a28d-941fb33f7ad2/274ec7ec93306a65.jpg"/></td><td><img src="https://zebfdsytobcavmuynuhx.supabase.co/storage/v1/object/public/review-images/tasks/9e598ea2-5465-454a-a28d-941fb33f7ad2/4ee02b456bf1496f.jpg"/></td><td><img src="https://zebfdsytobcavmuynuhx.supabase.co/storage/v1/object/public/review-images/tasks/9e598ea2-5465-454a-a28d-941fb33f7ad2/d12a2ed8fc8e8e1d.jpg"/></td></tr><tr><td>A.调控滴定速度</td><td>B.用pH试纸测定溶液pH</td><td>C.加热试管中的液体</td><td>D.向试管中滴加溶液</td></tr></table>
A