load ``BRCA_data_for_Problem_2.Rdata" and you will see a Data object. The Data object is a list consisting of data and subtype. data is a data.frame with 2000 rows (genes) and 610 columns (samples). The subtype is the subtype of breast cancer for each sample (three subtypes in total, Her2, Basal or LumA_LumB). Please note that the data has already been normalized and log-transformed, which means you don't need any preprocession of the data. In question a-d, we will do differentially expressed (DE) analysis and visualize the result. DE analysis is to find which gene expresses differently between two conditions (here the subtypes are our conditions). In this homework, I give an intuitive step-by-step instruction to finish DE analysis (See Question (a) below). The way I give below is obviously superficial but it is intuitive and enough for this homework. (a) Use all samples with subtype Her2 and LumA_LumB to do a differentially expressed (DE) analysis. Below are simple steps to do DE analysis. 1): For each gene, calculate the mean(Her)-mean(LumA_LumB), this is the log fold change you will use later. 2): For each gene, do a two sample t-test using t.test(Her2, LumA_LumB) and extract the p value. After step 1)