You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "when does the heart begin to beat in prenatal development?" whose answer is by week 4.
Each document should contain about 30 words, and these documents should contain useful information.

Query: when does the heart begin to beat in prenatal development
Useful Output:

Doc 1: The heart begins to pump fluid and then blood through the blood vessels at about 5 weeks (3 weeks after fertilization). Most other organs begin to form at about
Doc 2: At 6 weeks gestation, the embryo has a steady heartbeat around 110 beats per minute! The heart moves oxygen-carrying blood throughout the developing embryo.
Doc 3: Cardiac activity will start by week 5 of pregnancy, but a fetal heartbeat doesn't develop more fully until weeks 17 to 20.
Doc 4: In Week 6, your baby's heart starts beating, and their brain develops rapidly. You may feel stronger symptoms like nausea and cravings.
Doc 5: At six weeks of pregnancy, an ultrasound can detect a little flutter in the area that will become the future heart of the baby.