add the sentence that best introduces the paragraph.\nthe tip of the pen has a tiny metal ball. this ball…

add the sentence that best introduces the paragraph.\nthe tip of the pen has a tiny metal ball. this ball rolls when you move the pen on paper. inside the pen, there is a tube filled with ink. as the ball rolls, it picks up the ink and spreads it onto the paper. the ball also acts like a kind of cap, which keeps the ink from leaking and from drying out too quickly.\na ballpoint pen is a writing tool with a smart design.\nink pens are fun to use and come in many colors.\nlong ago, people wrote with bird feathers instead of pens.\npeople often get ink on their hands when they use a pen.

add the sentence that best introduces the paragraph.\nthe tip of the pen has a tiny metal ball. this ball rolls when you move the pen on paper. inside the pen, there is a tube filled with ink. as the ball rolls, it picks up the ink and spreads it onto the paper. the ball also acts like a kind of cap, which keeps the ink from leaking and from drying out too quickly.\na ballpoint pen is a writing tool with a smart design.\nink pens are fun to use and come in many colors.\nlong ago, people wrote with bird feathers instead of pens.\npeople often get ink on their hands when they use a pen.

Answer

Brief Explanations:

The paragraph focuses on the design and working - mechanism of a ballpoint pen. The first option, "A ballpoint pen is a writing tool with a smart design", best introduces the paragraph as it sets the context for the description of the pen's features that follow. The other options are either about ink pens in general, writing tools in the past, or a common issue with pens, which are not the main focus of the given paragraph.

Answer:

A ballpoint pen is a writing tool with a smart design.