Refer to the Scenario Below to Answer the Following Questions

Refer to the scenario below to answer the following questions.
Zhang Lei began making wooden writing utensils as a hobby until Wang Hui recognized Zhang's talent. Wang immediately ordered 250 pens and pencils of various styles to be displayed in his shop's showcase. Within three months, the writing utensils were a hit! Zhang had never thought of marketing his talent but Wang's enthusiasm and the recent sales were enough to change his mind.
With limited resources, Zhang contacted three additional specialty shops within 100 km. He explained his manufacturing processes and engraving options to each. All three shops' owners placed a trial order. Within two months, just prior to the holiday season, each shop owner placed an additional order. Zhang was ecstatic!
"I figured business would slow down after that," Zhang stated, "but in February I was contacted by Penguin Pens Distributors. At that point, I had to make a huge decision about how far I wanted to go with this business."
Penguin Pens Distributors provided products for school fundraisers in the Beijing and Shanghai area. Zhang was offered a two-year contract and immediate inclusion in Penguin's promotional flyer. Zhang accepted the offer and, along with it, the responsibility to produce thousands of wooden pens and pencils.
"I had to get a grip on the magnitude of this project!" Zhang added. "I couldn't grow out of control. I was already working to capacity."
Zhang decided to place his major focus on the large contract with Penguin. However, to avoid placing his total emphasis with one customer, Zhang continued nurturing his four previously established accounts without targeting any additional customers.
"At this point, I had set up an assembly line in a rented building," Zhang explained. "I had to hire three full-time employees to work the line while I managed the customer orders and purchased materials." Zhang paused. "But I can't take the Penguin project for granted. It might not always be there. I'll have to have a good alternate plan if that day comes."
-In marketing his writing utensils to his four specialty-shop customers,Zhang Lei is using ________ marketing.

A) mass
B) undifferentiated
C) niche
D) mass customization
E) individual