To solve this problem, we need to determine what percentage of the lymphoid tissue in the human body is constituted by MALT (Mucosa-Associated Lymphoid Tissue).$\newline$Let's analyze the options:$\newline \bullet$Option 1: 20$\% \newline \bullet$Option 2: 70$\% \newline \bullet$Option 3: 10$\% \newline \bullet$Option 4: 50$\% \newline$MALT is a significant component of the immune system, associated with mucosal surfaces. It includes structures like the tonsils, Peyer's patches, and the appendix.$\newline$Research and studies indicate that MALT constitutes about 50$\%$ of the lymphoid tissue in the human body.$\newline$Therefore, the correct answer is Option 4: 50$\%$.