This task involves annotating the answer type to a given question that involve some kind of complex reasoning (including numerical reasoning). Note that the questions require looking at more than one part of the passage to answer. There are 3 possible answer types (i) spans, (ii) numbers and (iii) dates. If the answer can be found in the passage, label it as "span". If the answer is a number, label as "number". Similarly, label "date" if you think the answer to the given question is a date.

Passage: Coming off their divisional home win over the Texans, the Titans stayed at home for a Week 14 intraconference duel with the San Diego Chargers. In the first quarter, the Titans went on the attack first as kicker Rob Bironas managed to get a 44-yard field goal for the only score of the half. In the third quarter, the Chargers tied the game with kicker Nate Kaeding getting a 20-yard field goal. Afterwards, Tennessee would regain the lead with rookie RB Chris Brown getting a 7-yard TD run. In the fourth quarter, the Titans increased its lead with RB LenDale White getting a 7-yard TD run. However, San Diego tied the game with QB Philip Rivers completing a 7-yard TD pass to RB LaDainian Tomlinson and a 2-yard TD pass to TE Antonio Gates. In overtime, the Chargers sealed the win with Tomlinson getting a 16-yard TD run. The Titans have lost 4 out their last 5 games since starting the year at 6-2.
Question: How many touchdown passes did Philip Rivers throw in the fourth quarter?
number