The verb to lend means to give something to someone for a short time, expecting that they will give it back to you later.

This verb fits the meaning and grammar of the sentence, as it expresses a polite request to use someone’s pen temporarily.

The other options are incorrect because they do not match the meaning or grammar of the sentence.

Option A. borrow is incorrect because it means to take something from someone for a short time, with their permission and with the intention of giving it back later. This verb should be used by the person who wants to use the pen, not by the person who has the pen.

Option B. loan is incorrect because it means to give money or property to someone who agrees to pay it back with interest. This verb is usually used for more formal or long-term transactions, not for casual or short-term requests.

Option C. provide is incorrect because it means to supply or make available something that someone needs or wants. This verb does not imply that the person who provides something expects to get it back later.

Therefore, the correct answer is D. lend.

The sentence with the correct word filled in is: I forgot to bring a pen with me. Would you, please lend me yours?