A、In the 1830s. B、In the 1930s. C、In the 1860s. D、In the 1960s. A短文提到，19世纪30年代，当德国科学家Frederick Tiedmann提出“脑子的大小和智力有关联”时，人们开始关注脑子

People with bigger brains tend to score higher on standard tests of intelligence, according to new study findings. [19]However, study author Dr. Michael A. McDaniel emphasized that these findings represent a general trend, and people with small heads should not automatically believe they are less intelligent. For instance, Albert Einstein’s brain was "not particularly large", McDaniel noted. "There’s some relationship between brain size and intelligence on average, but there’s plenty of room for exceptions," he said. [20]Inter-est in the relationship between brain size and intelligence grew in the 1830s, when German scientist Frederick Tiedmann wrote that he believed "there was a connection between the size of the brain and the mental energy displayed by the individual man". Since that statement, scientists have conducted numerous studies to determine if Tiedmann’s argument was, in fact, correct. More recently, researchers have published additional studies on intelligence and brain size. For his study, McDaniel analyzed more than 20 studies that investigated the relationship between brain size and intelligence in a total of 1,530 people. The studies showed that on average, people with bigger brains tended to be more intelligent. The relationship between brain size and intelligence was stronger in women than men, and in adults than children, Mc-Daniel noted. In an interview, McDaniel noted that he’s not sure why the relationship was stronger for adults and women. Previous research has shown that women, on average, tend to have smaller brains than men, but score just as well—if not higher—in tests of intelligence, he said.
19 What does Dr. McDaniel believe?
20 When did the study on the relationship between brain size and intelligence become popular?
21 What can we infer from the previous research mentioned in the passage?