It's difficult to estimate the exact number of boys in Javier's grade who feel insecure about their bodies, as this can vary depending on factors such as cultural norms and individual experiences. However, research suggests that body dissatisfaction is a common issue among boys and girls of all ages, and it's likely that a significant proportion of Javier's classmates share his feelings.
Based on this, the answer is likely (C) three-quarters, meaning that about 75% of boys in Javier's grade may have similar feelings about their shapes.
As for the second question, children begin to understand body weight and size at a very young age, and this understanding continues to develop over time. Research suggests that by age 3 or 4, children may begin to show awareness of their own body shape and size, and may even begin to express concerns about their weight or appearance. Therefore, the answer is (B) four years old.