Here's what Marissa Mayer told upset investors asking about Yahoo's decline

Yahoo's business has been in years of decline lately, and some investors are not happy about it.

And during Yahoo's annual shareholder meeting on Thursday, one frustrated investor went straight to Yahoo CEO Marissa Mayer to ask about it.

Mayer's answer: it's a competitive space but we're investing in growth.

"We're in a very competitive space, so we've invested in our products to make sure that we attract the maximum number of users and the maximum amount of their time and energy each day," Mayer said during the meeting.

Mayer stressed that Yahoo drives most of its revenue through digital advertising, and some parts of the online advertising business, like banner ads, have been in a secular decline over the past few years, as seen in Yahoo's shrinking desktop revenue.

Yahoo has been aggressive on the mobile advertising front, investing in two major products, Gemini and Brightroll, to beef up its mobile, native, and video advertisement offerings. Mayer reiterated the fact that Yahoo's "Mavens" business - short for mobile, video, native and social - was almost non-existent when she first joined the company, yet it's now generating $1.6 billion in annual revenue. (Although Mavens' growth has also turned sluggish in recent quarters.)

"These are some of the elements on the strategic plan that we're executing to try and correct for the lack of growth," Mayer said.

Mayer declined to make any comment on the Yahoo's core sales process during the meeting. But she did acknowledge that it's "continuing to make great progress" and that she's "heartened by the interest in Yahoo." Recent reports suggest companies like Verizon, AT&T, and some private equity firms have expressed interest in buying Yahoo's core internet properties.

"It validates our business progress and achievements to date," Mayer added.